29 Nutritional Adaptation in Man

Dr. Meenal Dhall

Contents:

1. Introduction

1.1 What is nutrition

1.2 Main nutrients essential for human body

1.3 Energy requirements of human

2. Nutritional adaptation

2.1 Lactose intolerance

3. Comparative dietary and nutritional adequacy

3.1 Hunters and gatherers

3.2 Agriculturalists and pastoralists

3.3 Protein and population density association

4. Nutritional adaptation in extreme environments

4.1 Nutritional adaptation in high altitudes

4.2 Nutritional adaptation in cold climate

4.3 Nutritional adaptation in hot climate

5. Summary

Learning objectives:

To understand what is nutrition, the main nutrients essential for human body
To understand the Energy requirements of human
To understand the nutritional adaptation with the example of lactose intolerance
To understand Comparative dietary and nutritional adequacy of hunters and gatherers and of agriculturalists and pastoralists
To understand the association between protein and population density
To understand Nutritional adaptation in extreme environments- in high altitudes, cold climate and in hot climate.

Introduction:

1.1 What is nutrition – The Nutrition is can be defined as the process of taking in food and using it for growth, metabolism, and repair. In other words nutrition or nourishment is the supply of food required by organisms to remain alive. There are five nutritional stages they are ingestion, digestion, absorption, transport, assimilation and excretion. Good nutrition is a well balanced diet combined with regular physical activity and it is very important for the good health. Poor nutrition can cause reduced immunity, increased sensitiveness to diseases, reduced physical and mental development. Today as molecular biology, biochemistry and genetics advanced, nutrition has become more focused. Nutrition deals with the identifying how certain diseases or problems may be caused by dietary factors, such as poor diet (malnutrition), food allergies, metabolic diseases, etc. Nutrition also focuses on how diseases and problems can be lessened or can be prevented with a healthy diet.

1.2 The main nutrients essential for human body –

A nutrient is a source of the nourishment in a food. According to Medical News Today, the human body requires majorly seven types of nutrients. They are carbohydrates, fat, protein, fiber, vitamin, mineral, and water. Nutrients can be divided into two categories- micronutrients and macronutrients, Macronutrients are nutrients that are required in relatively large extent. Micronutrients are nutrients that are required in relatively small extent. Most of the foods contain a combination of some or sometimes all of the seven nutrients. We need some nutrients regularly and others less repeatedly. Poor health may be cause by either due to deficiency or due to excess of nutrients.

Energy giving macronutrients– these nutrients provide energy to the human body, these measured in kilocalories (kcal) or Joules

(J). (1kcal=4185.5 joules).

Carbohydrates: Molecules of carbohydrates consists of carbon, hydrogen and oxygen atoms. Carbohydrates can be monosaccharide (glucose, fructose, glactose), disaccharide and polysaccharide (starch). Polysaccharides are more aided for human because they are more complex sugar chains and take longer time to breakdown and absorb into the blood. Excessive increase in blood sugar levels are linked to heart and vascular diseases.
Proteins: Molecules of proteins contains nitrogen, carbon, hydrogen and oxygen. Simpler proteins are called monomers are together forms complex proteins called polymers, which functions in building and repairing of tissue. When proteins are used as a fuel is required to break down, as it breaks down into nitrogen, which is eliminated by the kidneys.
Fats: Fats are triglyceride it is consists of three molecules of fatty acid combined with a molecule of the alcohol glycerol. Fatty acids are monomers, simple compounds and the triglycerides are polymers complex compounds.

Other macronutrients- these do not provide energy.

Fiber: fiber consists of majorly of carbohydrates. Because of its limited absorption by the body, the sugars and starches not much get into the blood stream. Fiber is essential part of human nutrition.
Water: near about 70% of the mass of the human body is water (Medical News Today). How much water the human body needs nobody is completely sure. The claims vary from between one to seven liters per day to avoid dehydration. Water requirements are very closely associated to body size, age, physical activity, environmental temperatures, different states of health, and dietary patterns of the people. The people who consume a lot of salt will require more water than those who consumes less salt even if they both are of the same height, age and weight, exposed to the same levels of external temperature (Medical News Today).

Micronutrients – these nutrients required in relatively small quantities throughout a person’s life.

Minerals: the term “minerals” is misleading, and it would be more relevant if called “dietary ions” (Medical News Today). The experts at the University of Florida say that 16 key minerals are important for the human biochemical processes by serving functional and structural roles and also as electrolytes.

Potassium: it is systemic electrolyte, essential in co-regulating ATP (an important carrier of energy in cells in the body) with sodium. Deficiency leads to hypokalemia and excess leads to hyperkalemia.
Chloride: it is crucial for hydrochloric acid production in the stomach and also important for the cellular pump functions. Deficiency leads to the hypochloremia and excess leads to hyperchloremia.
Sodium: it is a systemic electrolyte it is essential in regulating ATP with potassium. Deficiency leads to the hypoatremia (causes cells to malfunction; extremely low sodium can be fatal). Excess leads to the hyperatremia. According to The American Heart Assosiciation (AHA) the sodium consumption should be limited to 1500 milligrams per day.
Calcium: it is important for the muscle, heart and digestive health. It is important for building bones, help in the synthesis and function of blood cells. Deficiency leads to the hypocalcaemia (spasms and hyperactive deep tendon reflexes, muscle cramps, abdominal crapms) Excess leads to the hypercalcaemia (constipation, muscle weakness, also it may affect conduction of electrical impulses in the heart, calcium stones in the urinary tract, impaired kidney function and impaired absorption of iron leading to iron deficiency).
Phosphorus: it is one of the components of bones and also play important role in energy processing. Deficiency of phosphrous leads to hypophosphatemia, an example of hypophosphatemia is rickets. Excess of phosporous leads to the hyperphosphatemia, results of kidney failure.
Magnesium: it helps in processing of ATP and required for healthy bones. Deficiency of magnesium leads to the hypomagnesemia (irritability of the nervous system with spasms of hands and feet, muscular twitching and larynx spasms). Excess of magnesium leads to the hypermagnesemia (vomiting, nausea, impaired breathing and low blood pressure.
Zinc: it is necessary for several enzymes. Deficiency of zinc leads to the short stature, anemia increased pigmentation of the skin, impaired gonadal function, enlarged liver and spleen, impaired wound healing and immune deficiency. Excess of zinc leads to suppression of copper and iron absorption.
Iron: it is required for proteins and several enzymes. Deficiency of iron leads to the anemia. Excess leads iron leads to the iron load disorder. Iron deposits can occur in organs, particularly in the heart
Manganese: it is a cofactor in enzymatic functions. Deficiency of manganese leads to the fainting, hearing loss, weak tendons and ligaments. Excess of manganese interferes with the absorption of dietary iron.
Copper: it is crucial component of many redox enzymes. Deficiency of copper leads to the anemia or pancytopenia (it is reduction in the number of red and white blood cells, as well as platelets) also it may leads to neurodegeneration. Excess of copper interfere with the formation of blood cellular components in the body.
Iodine: it is essential for the biosynthesis of thyroxine (a form of thyroid hormone). Deficiency of iodine leads to developmental delays problems. Excess of iodine leads to malfunctioning of thyroid gland.
Selenium: it is essential cofactor to activity of antioxidant enzymes. Deficiency of selenium leads to the Keshan disease (myocardial necrosis leading to the weakening of the heart), Kashing-Beck disease (atrophy degeneration and necrosis of cartilage tissue). Excess of selenium leads to the garlic-smelling breath, gastrointestinal disorder, sloughing of nails, hair loss, fatigue, irritability and neurological damage.
Molybdenum: it is the important part of the three enzyme systems- xanthine oxidase, aldehyde oxidase and sulfite oxidase. It has a important role in iron utilization in carbohydrate metabolism and in uric acid formation. Also it has important role in sulfite detoxification. Deficiency of molybdenum may affect metabolism and blood cell counts but as this deficiency is often alongside other minerals deficiencies, such as copper. There is a little data on toxicity caused by excess of molybdenum.

Vitamins: there are the organic compounds that we require in small amounts. Vitamins are classified into two- water soluble vitamin (dissolve in water) or fat soluble vitamin (they can dissolve in fat). A total of 13 Vitamins essential for human body (Medical News Today). For humans there are 4 fat-soluble (A, D, E and K) and 9 water- soluble (8 type of vitamins B and vitamin C). Water soluble vitamins required to be consumed more regularly because they are easily eliminated faster and are not readily stored in the body. Urinary output is a very good predictor of water soluble vitamin consumption. Several water-soluble vitamins are synthesized by bacteria. Fat-soluble vitamins are absorbed through the intestines with the help of fats or lipids. They are easily accumulated in the body because they are harder to eliminate quickly. Excess levels of fat-soluble vitamins are more common than with water soluble vitamins – this condition is called hypervitaminosis. Patients with cystic fibrosis require to have their levels of fat-soluble vitamins carefully monitored.

Vitamin A: chemical names of Vitamin A are retinol, retinoids and carotenoids. It is Fat-soluble vitamin. Deficiency of vitamin A leads to Night-blindness. Overdose of vitamin A leads to ketomalacia (degeneration of the cornea).
Vitamin B1: Chemical name of Vitamin B1 is thiamine. It is Water soluble vitamin. Deficiency of this can cause diseases like- beriberi, Wernicke-Korsakoff syndrome. Overdose of Vitamin B1 are rare hypersensitive reactions resembling anaphylactic shock when overdose is due to injection
Vitamin B2: chemical name of Vitamin B2- riboflavin. It is Water soluble vitamin. Deficiency of Vitamin B2 can cause disease- ariboflanisosis (mouth lesions, seborrhea and vascularization of the cornea.
Vitamin B3: chemical name of Vitamin B3 is niacin. It is Water soluble vitamin. Deficiency of Vitamin B3 can cause disease- pellagra. Overdose of Vitamin B3 leads to liver damage, skin problems and gastrointestinal complications.
Vitamin B5: chemical name of Vitamin B5 – pantothenic acid. It is water soluble vitamin. Deficiency of Vitamin B5 causes disease- paresthesia (tingling, pricking or numbness of the skin with no apparent long term physical effect).
Vitamin B6: chemical name of Vitamin B6 – pyridoxamine, pyridoxal. It is Water soluble vitamin. Deficiency of this causes – anemia. Overdose can causes nerve damage, proprioception is impaired (it is ability to sense stimuli within your own body are decreased).
Vitamin B7: chemical name of Vitamin B7- biotin. It is Soluble in water. Deficiency of this can cause disease – dermatitis, enteritis.
Vitamin B9: chemical name of Vitamin B9- folinic acid. It is Soluble in water. Deficiency of this can cause – birth defects during pregnancy, such as neural tube.
Vitamin B12: chemical name of Vitamin B12 – cyanocobalamin, hydroxycobalamin, methylcobalamin. It is Soluble in water. Deficiency of this can lead to disease – megaloblastic anemia (red blood cells without nucleus).
Vitamin C: chemical name of Vitamin C – ascorbic acid. It is Soluble in water. Deficiency of this can cause disease – scurvy. Overdose of this may cause – diarrhea, nausea, skin irritation, burning upon urination, depletion of the copper and it increases the risk of kidney stones.
Vitamin D: chemical name of Vitamin D- ergocalciferol, cholecalciferol. It is Soluble in fat. Deficiency of this causes disease like – rickets, osteomalacia (softening of bone), recent studies indicate higher risk of some cancers. Overdose of this causes – hypervitaminosis D (headache, disturbed digestion, weakness, and tissue calcification also may leads to increased blood pressure).
Vitamin E: chemical name of Vitamin E – tocotrienols. It is Soluble in fat. Deficiency of this leads to include hemolytic anemia in newborn babies. Overdose of this can higher risk of congestive heart failure.
Vitamin K: chemical name of Vitamin K – phylloquinone, menaquinones. It is Soluble in fat. Deficiency of this may increase tendency to bleed. Overdose of this may induce the effects of warfarin.

1.3 Energy requirements of human: basal or resting metabolism is used as fundamental assessment of human energy needs. This is measured while the individual is totally inactive and thermally neutral. It is considered an assessment of the energy conversion required for important functions. This includes the energy used by such continuous functions like the neural, cardiovascular, respiratory and liver functions and also energy consumed for the survival of other body cells. The amount of energy expended in basal metabolism is higher during growth and in women during pregnancy and lactation because of high cell multiplication rates. The basal metabolism of an average size young adult male is of 300 kJ/hr, but may be higher in pregnant and lactating women (around 400 kJ/hr), and as low as 150 kJ/hr in young children. This result in individual energy requirement variation from 3600 to 9600 kJ per day in basal requirements. Living in hot or cold environment also affects the energetic requirements

Nutritional adaptation: it is observed that not all people can survive well at high altitude or under intense ultraviolet radiation. Similarly, there are major differences around the world in how effectively our bodies process particular type of food. In addition, some people live favorably on daily diets that would be at a starvation level for others. Different human populations not only eat different foods but their digestive systems works in different ways. For instance, the Inuit of Alaska, Northern Canada, and Greenland traditionally ate far more fat than most other populations and their gastrointestinal systems apparently are more competent of breaking fats down for use by their bodies. This indicates that adapting to local nutritional fitness has led to the evolution of related genetic differences among the populations of the world. Many Indians in the Southwestern United States have what have been described as “thrifty genes.” (xxxx) Their bodies are unusually efficient at utilizing the calories in their food thus they need to consume less than other people of their size in order to maintain a stable weight.

For example Tohono O’ Odham Indians of Southern Arizona.

2.1 Lactose intolerance: The best documented differences in nutritional adaptation relates to milk or lactose. In the period of the following World War II, many of the most prosperous countries of the north temperate region, especially the United States, decided that the food shortages of many countries could be aided by food supplementation. Among the readily available food supplies in the temperate countries was milk, which was dehydrated and provided to many of the countries which are having food shortages. By the 1960s, it was observed that in many of the populations these food supplements often resulted in widespread diarrhea and further research showed that many adults developed a diarrhea when they ingested significant quantities of milk. Later research showed that a major population of world’s population cannot digest the lactose contained in fresh milk products because of the lack of an enzyme called lactase. This gut enzyme converts lactose to sugar which may be converted to energy in the normal biochemical chains.

Lack of this enzyme results in a loss of food energy and irritation of the intestine causing diarrhea and other undesirable effects. Infants and young children in all populations have this enzyme but in many groups this enzyme disappears in older children producing lactose-intolerance adults. The processes like fermentation involved in the production of yoghurt and cheeses break down lactose into a digestible form. Therefore the problem arises only when the populations (which lack lactase enzyme) use milk or its products in fresh form, such as milk, cream, or very fresh cheeses. The ability to produce lactase is genetically controlled. The gene that codes for this enzyme is present on chromosome 2(xxxx). The studies of lactose intolerance show that a population is best adapted to its traditional nutrient environment and therefore any change in that environment are likely to be stressful.

Comparative dietary and nutritional adequacy: According to Harrison, the diet of the early precursors cannot be directly determined but we can assume on its composition based on the diet of our nearest relatives, the apes and the preserved evidence of the early hominoid forms. The teeth and jaw structures of the earlier hominids indicates the best clues for their diet. In general teeth became smaller in the size in more recent forms but it did not show high degree of specialization. Some of the earlier hominoid forms developed teeth which are presumed to indicate a more vegetarian diet.

3.1 Hunters and gatherers: it was commonly thought, until quite recently, that during the evolutionary process hunting became an increasingly important food source (Harrison, 1988). The reasons for this belief were multiple, firstly most of the artifacts found utilized for hunting and animal slaughtering. Secondly early cave arts and there is evidence for the religion focused on hunting. Even the contemporary world, most populations prefer a high meat diet (Harrison, 1988). While hunting and meat eating were important in the early human diet, recent research indicates that meat was never the major energy source at any stage of human evolution (Harrison, 1988). In addition, such groups quickly substitute food items to their diet when regular trade was established. For these reasons it makes doubtful that quantitative nutritional information on the diet of hunters and gatherers before the development of agriculture. Throughout the 1960s the diet of some San in the Southern Africa remained relatively unaffected by the external factors (Harrison, 1988). The diet of the Kung San has been incompletely analyzed for nutrients. For this group meat contributed less than one third of the daily energy intake and their foods were diversified during the season of the dietary survey. According to Lee, 1979 noted that, in their food over 20 species of roots, melons, bulbs, and dried fruits were included. A similar diversity of food has been reported for most of the hunters and gatherers (Harrison 1988). It thus appears that the diets of the hunters and gatherers must have been nutritionally balanced and also the common deficiency diseases found in more recent populations were absent or quite rare in the hunters and gatherers (Harrison 1988).

3.2 Agriculturalists and pastoralists: Early agricultural societies with limited domesticated plants also continued to rely on the animals for certain important nutrients (Harrison 1988). Only these populations developed large enough to support the large villages, craft specialization and the beginning of urbanization and civilization. The nutritional sufficiency of the plant and animal complexes are not similar and the kinds of the nutritional deficiencies varied according to their basic crops. The highly populated areas of Euresia had a diversity of domesticated animals and the crops (Harrison 1988). The wheat and millet contains carbohydrate and protein. Various fruits and vegetables provided sufficient minerals and vitamins. The rice based food complex extending from Japan and Korea, south to Indonesia and east to parts of India supported a population but had deficiency of vitamin B1. This deficiency is occurred because polished rice is quite deficient vitamin B1 (Harrison 1988). In America, the potato based diet of highland South America and maize based diet of Mesoamerica supported almost 90 per cent of the hemisphere population (Harrison 1988). Out of the two the South America complex was nutritionally more secure for various reasons. Firstly, the potato is high in carbohydrate but low in proteins. Potato diet was supplemented by seed producing chenopodia that contains more proteins than wheat (Harrison 1988). Secondly, in the highland areas had the reasonable supplies of meat (Harrison 1988). Clear evidence shows in this area under-nutrition is very common as a consequence of its currently poor economic status (Harrison 1988). Maize crops contain a better amount of protein than root crops such as potatoes but it is lesser compared to the chenopodian or wheat (Harrison 1988). Domestic varieties of beans were a major crop and an important protein supplement, but the main problem was the lack of appropriate domesticated animals. In central Mexico, dogs and turkeys were raised as food. In fact, special hairless breeds of dogs were developed for cooking (Harrison 1988). Maya was another maize-based population which may have been affected by nutritional problems (Harrison 1988). The most concrete evidence that the maize –based diet can lead to niacin deficiency, the basic food stuffs are very low in niacin, and in the times of economic distribution the symptoms of pellagra become common (Harrison 1988). In the early 1900s the lower classes of the southern United States who had a maize- based diet had a high incidence of this serious nutritional deficiency disorder (Harrison 1988).

3.3 Protein and population density association: while by year 1500 most of the population centres had developed to various degrees. The vast majority of agriculture populations continued to depend on the foraging to provide a significant part of their diet that is why the density of the population supported by the particular system is closely linked with the availability of fishes, edible mammals, and milk and its products (Harrison 1988). Many authors have assumed that protein with the required complement of amino acids was the key element (Harrison 1988). The diets based on only a few plant sources may results in a number of serious deficiency syndromes. The early explores found among the maize-growing population American Indians of the eastern United States the largest densities are around fish rich waters such as Narranganst Bay in Rhode Island and the Brackish Chesapeake Bay (Harrison 1988). Populations in sub-Saharan Africa provide equally interesting examples of protein population density association (Harrison 1988). It might be argued that people simply find the taste of the meat is desirable (Harrison 1988). On the other hand some societies rate the value of the fish in relation to its relative fatness. So it can be concluded that in the evolutionary process the genetic development of taste for fat has been genetically selected and the humans seek to capture food which provide nutrients crucial for their survival and well being (Harrison 1988).

4. Nutritional adaptation in extreme environments: An extreme environment can be defined as an environment where basic needs of human beings like collection of food, shelter and protection require intense efforts. One important feature of these environments is that an error in judgment can cause serious consequences (Brubakk 2000). When faced with hot, cold, high altitude (terrestrial heights above 2700 meters), and human beings either try to modify the environment accordingly or adapt their physiology to fit the environment or it may use a combination of these two strategies. The diet of humans varies in quantity and composition in different climatic regions. Although much of this variation may be due to availability of food in that area, selection of certain types of foods or adaptation to some of the dietary habits, which can help in acclimatization process in that particular environment. Most of the studies on relationship of extreme environment and diet are the outcome of military research or expeditions to mountains and Polar Regions. Under these types of conditions high energy expenditure not always compensated by adequate energy intakes

(Edwards & Roberts 1991, Shephard 1991).

4.1. Nutritional adaptation in high altitudes: there are 140 million permanent inhabitants of High Altitudes in the Himalayas, Central Asian, East African Andean and Rocky mountainous regions (Moore 2001). Permanent residency is restricted to about 4300m, although some ethnic groups e.g. miners in the Peruvian Andes are reported to live at heights of 5500m for a short period of time. High Altitudes presents an extreme conditions like hypoxia, high solar radiation, cold, also there is the psychological stress. The high altitude areas are also arid in nature with sparse vegetation and shortage of drinking water. These factors can vary in magnitude depending upon the location of the area and season of that area.

4.1.1. Food Intake and Energy Requirements in high altitudes: Many studies have shown that individuals loose significant amounts of body mass during a climb to or a stay at High Altitudes. Weight loss in high altitudes is mainly caused by malnutrition probably due to hypoxia (Bhardwaj et al. 1995, Westerterp 2001). Calories consumption can get reduced by 40% at high altitudes resulting in negative nitrogen balance (Hannon et al. 1976, Surks et al. 1966, Johnson et al. 1969, Whitten & Janoski 1969). High Altitudes exposure leads to the reduction in calories consumption and it is coupled with increased metabolic rate this considered as a major cause of weight loss (Butterfield et al. 1992). The taste thresholds for sweet and salt modalities have been found to be elevated whereas for bitter and sour modalities were reduced (Singh et al. 1997). The leptin levels also decreases at High Altitude and it is considered major cause of anorexia (Tschop et al,1998).

4.1.2 Nutrients requirement at high altitudes: Carbohydrates: High carbohydrate diets are beneficial at High Altitude (Kayser 1992). Carbohydrates provide higher energy per mole of oxygen. Diets high in carbohydrates are shown to enhance the glucose metabolism at high altitude. Studies on Indian residents at High Altitudes show that up to 60% energy is derived from carbohydrates (Sridharan et al.1995). Proteins: Negative nitrogen balance is reported at High Altitude by Consolazio et al. (1963) and Surks et al. (1966). In a well controlled study with 12 g/day dietary nitrogen intake has shown positive balance (Sridharan et al. 1982). After acclimatization there is no alteration in protein metabolism at high altitude when intake of food was adequate with protein at sufficient level was ensured. Fats: After acclimatization at high altitude for two years Rai et al. (1975) have studied utilization of fat by feeding up to 325g/day and found 95.5% fat digestibility with almost constant levels of fecal fat. In controlled study conducted by Sridharan et al. (1982) no adverse effect on digestion under High Altitude was observed. Iron: The requirements of increased haemoglobin synthesis during initial phase of stay at High Altitude are fulfilled by redistributing body stores and from dietary iron. Urinary excretion of Zn2+ is more during physical exertion as observed during an expedition to Mount Everest (Rose et al.1988). Zinc: Reduced zinc levels can lead to the anorexia. Zinc supplementation has been found to be beneficial in women mountaineers in controlling weight loss and their leptin levels also remain unchanged (Suri et al.2002).

4.2. Nutritional adaptation in cold environment: For providing nutritional support in a cold environment energy requirements are the main consideration (Askew 1989). Exposure to cold increases energy requirements. Energy requirements in cold environment are influenced by various factors like the intensity of the cold, speed of wind, physical factors (like melting of snow etc). Johnson and Kark (1947) have reported that individuals in cold climate normally eat more than those in warm climate. Gray et al. (1951) have suggested that increased energy requirements are caused due to ‘hobbling’ effect of the weight of clothing (7-10 kg) and associated with efforts of locomotion. As technology has improved the weight of cold weather clothing has decreased, however clothing is still a considerable burden. It appears that heat loss in a cold environment is can be reduced through clothing and behavior (i.e. seeking shelter whenever possible, creating or moving to warmer environments). Also, skeletal muscle contractions, either during voluntary exercise or involuntary shivering are the major source of metabolic heat produced to protect against cold stress. Severe losses of body weight in a cold environment complicate the normal physiology of the body. Thus it is important during physically active conditions to maintain the adequate intake. There is a common belief that cold climate conditions lead to an increased appetite. However the reported increase in appetite is also associated with changes in other aspects of individual’s environment such as increased activity levels, energy expenditure due to thermo genesis, social isolation and modification in the diet. In animals increased energy expenditure caused by increased thermo genesis due to cold environment is compensated by increased intakes (Louis-Sylvestre 1987).

4.2.1 Fat metabolism in cold environment: Humans can adapt in cold environment over a period of time to a high fat diet. Various Indian Antarctic expeditions have common observation of increase in body weight that is mainly due to increased intake. Several factors are responsible for an enhanced appetite in cold regions includes cold temperature, palatability of food, changes in physical activity habits and emotional factors (e.g. loneliness). The low leptin levels may be responsible for increased food intake. The dietary pattern of natives of arctic and sub arctic regions and their obvious success in coping with harsh environment have influenced arctic explorers to choose diets high in fat in general belief that this may be helpful for their adaptation. Such information is largely anecdotal and probably relates more to the availability of local foods (seal, fish, and whale) and familiarity of Eskimos with these foods. However such diets are rich in fatty acids, which play important role in prevention of cardiovascular diseases (Ulbricht & Southgate 1991). There is evidence to suggest that stimulation of carbohydrates oxidation by ingestion of an ephedrine-caffeine mixture and it can help to improve cold tolerance in humans (Vallerand et al. 1989).

4.3. Nutrition adaptation in hot environment: in the hot environment adequate fluid replacement overshadows all other considerations of nutrient requirements. Drinking adequate water in heat prevents dehydration, heat illness and reduced performance. Hypohydration depends in large part upon sweat rate, which is in turn determined by workload and duration. Other environmental factors are solar load, wind speed, relative humidity and clothing (Shapiro et al. 1982). In hot environment energy expenditure is increased by a small but significant amount because of additional work of increased sweat gland activity and ventilation. Consolazio et al. (1963) estimated that there is rise of approximately 10% in energy requirement at the temperature of 38oC. Excessive nitrogen losses are reported in perspiration of unacclimatized people but not in acclimatized people (Shworth & Harrower 1967).

4.3.1. Micronutrient requirements in hot climate: There is no extra need of iron and vitamins in hot environment (Micksen & Keys 1943). Although loss of water-soluble B-vitamins is minimal a deficiency could occur over time from profuse sweating coupled with an insufficient dietary intake. Thiamine, riboflavin, niacin and Vitamin B6 are important to energy metabolism thus it is important the level of these vitamin intakes should be adequate to amount of food consumed. It was found that sodium chloride (NaCl) requirement increases due to loss in sweat; 15 to 16 gm of salt normally taken in diet is quite adequate for acclimatized people (Malhotra 1960). Supplementation of potassium in drinking water may enhance the process of acclimatization. Detailed studies on effect of consumption of brackish water of Rajasthan containing high levels of fluoride (1.47-2.67 parts per million) and nitrate (35-64 parts per million) have also been carried out. No adverse effect and symptoms of fluorosis upto two years of intake were noted in adequately nourished people although the excretion of fluoride was found high (Sridharan et al.1991).

Summary :

The Nutrition is the process of taking in food and using it for growth, metabolism, and repair.
Good nutrition is an adequate, well balanced diet combined with regular physical activity, it is very essential for the good health. Poor nutrition can lead to reduced immunity, increased susceptibility to diseases, impaired physical and mental development and reduced productivity.
Human body requires seven major types of nutrients. They are protein, carbohydrates, fat, vitamin, mineral, fiber and water.
Fundamental to the assessment of human energy needs is basal or resting metabolism. This measure of energy use is determined while the individual is totally inactive and thermally neutral. Individual energy requirement, which vary from 3600 to 9600 kJ per day in basal requirements.
There are major differences around the world in how effectively our bodies process particular type of food. Different human populations not only eat different foods but their digestive systems works in different ways.
The best documented differences in nutritional adaptation relates to milk or lactose. Lactase, lack of this enzyme results in a loss of food energy and irritation of the intestine causing diarrhea and other undesirable effects. Infants and young children in all populations have this enzyme but in many groups this enzyme disappears in older children producing lactose-intolerance adults.
Study indicates the diets of the hunters and gatherers must have been nutritionally balanced and the common deficiency diseases found in more recent populations were absent or quite rare.
The nutritional adequacies of the plant and animal complexes are not very uniform. The types of the nutritional deficiencies vary according to the basic crops.
The fish supply and population density in the Amazon basin and of the game supply and population in sub-Saharan Africa provide interesting examples of protein population density association.
Nutritional inadequacies often have a strong impact on the impact on the growth of children.
When faced with hot, cold, high altitude (terrestrial heights above 2700 meters), and human beings either try to modify the environment accordingly or adapt their physiology to fit the environment or it may use a combination of these two strategies.
The diet of humans varies in quantity and composition in different climatic regions.
Many studies have shown that individuals loose significant amounts of body mass during a climb to or a stay at High Altitudes. Weight loss in high altitudes is mainly caused by malnutrition probably due to hypoxia, the reduction in calories consumption and with increased metabolic rate.
High carbohydrate diets are beneficial at High Altitude Diets high in carbohydrates are shown to enhance the glucose metabolism at high altitude.
There is a common belief that cold climate conditions lead to an increased appetite. . Several factors are responsible for an enhanced appetite in cold regions includes cold temperature, palatability of food, changes in physical activity habits, reduction in leptin level and emotional factors (e.g. loneliness).
In hot environment energy expenditure is increased by a small but significant amount because of additional work of increased sweat gland activity and ventilation. There is rise of approximately 10% in energy requirement at the temperature of 38oC.
In hot environment it was found that sodium chloride (NaCl) requirement increases due to loss in sweat. Supplementation of potassium in drinking water may enhance the process of acclimatization.

you can view video on Nutritional Adaptation in Man