Malnutrition, Obesity, and Essential Nutrients
Malnutrition and Its Impact
Malnutrition encompasses several conditions:
- Too little food intake: Protein-calorie malnutrition (PCM), starvation, or insufficient quantity/quality of food.
- Too much food intake: Overabundance, leading to obesity.
- Poorly balanced diet: Chronic micronutrient malnutrition or an unbalanced diet.
Obesity is now a greater cause of death globally than malnutrition, with three times as many people dying from obesity.
Essential Nutrients
Nutrients provide energy and essential materials. These include:
- Macronutrients: Carbohydrates, proteins, and fats.
- Micronutrients: Vitamins and minerals.
Nutrient deficiencies often occur due to poor diet or reliance on limited resources.
Proteins and Amino Acids
Proteins have highly variable structures and functions, built from amino acids and peptides. When broken down, proteins can be used to create other amino acids (non-essential amino acids). However, some amino acids (essential amino acids) cannot be synthesized by the body and must be consumed. A deficiency in any essential amino acid leads to a general protein deficiency.
The traditional Mesoamerican diet (Maya/Aztecs and modern Mexico and Central America) includes beans and maize (corn). Consuming several plant sources reduces the risk of essential amino acid deficiencies. An example of an essential amino acid is lysine, while cystine is non-essential.
Energy Reserves
PCM involves a reduced total diet, leading to protein and energy deficiency. The body utilizes three types of energy:
- Glycogen: Stored glucose in the liver and muscles (short-term, preferred source).
- Fat: Lipid molecules (long-term, major energy storehouse).
- Protein: Broken down to provide energy and synthesize glycogen.
After glycogen and fat reserves are depleted, protein breakdown begins, affecting muscles and the immune system. Children are at greater risk, experiencing growth disruptions such as kwashiorkor (swelling, enlarged liver due to protein deficiency) and marasmus (muscle and fat loss, dehydration).
Children typically have similar growth patterns, requiring substantial protein for growth. Stunting (reduced linear growth) and wasting (low weight-for-height ratio) are common effects. Harris lines indicate slowed bone growth due to stress.
Overnutrition
Overnutrition leads to accelerated growth during childhood, early menstrual cycles, and decelerated growth during adolescence. This is not exclusively a developed-world problem.
“Buying time” is a short-term solution where central and reproductive systems are spared. There is no population difference in the ability to withstand starvation. The “thrifty genotype” hypothesis suggests that certain genes promote fat storage due to historical food scarcity.
Vitamin Deficiencies
- Vitamin A (Retinol): Derived from beta-carotene, stored in the liver. Deficiency leads to rhodopsin protein deficiency (night blindness) and epithelial issues (dry, scaly skin, brittle nails).
- Vitamin B1 (Thiamine): Important for carbohydrate and protein metabolism. Deficiency is common with high-carb diets, affecting neurotransmitter and myelin production. Milled rice lacks thiamine compared to unmilled rice. Beriberi disease can be “wet” (affecting the heart and circulatory system) or “dry” (affecting nerves and muscles).
- Vitamin C (Ascorbic Acid): Crucial for collagen production. Deficiency historically affected sailors, causing scurvy (swollen, bloody gums, loose teeth, bulging eyes). It is also observed in low-income populations.
- Vitamin D (Calcitriol): Stimulates calcium absorption in the small intestine and bone deposition. Deficiency leads to osteomalacia (poorly mineralized bones) and rickets.
Electrolytes and Mineral Deficiencies
Electrolytes are minerals with an electric charge, present in tissues and body fluids. The four basic types are magnesium, calcium, sodium, and potassium.
Iron deficiency is a prevalent nutritional problem, causing anemia (fatigue, neurological impairment). Iodine is needed to make thyroid hormone, regulating development and metabolism. Deficiency leads to goiters (overworked thyroid gland) and hypothyroidism.
Lactose and Lactase
Lactase activity decreases with age in mammals, leading to lactase restrictions (intolerance, malabsorption). Why can some populations digest lactose? Environmental factors, a history of farming, and a genetic mutation in the LCT gene, which controls lactase production, allow some individuals to produce lactase after childhood.
Lactase Persistence
Lactase persistence depends on carrying specific alleles in the LCT gene. The age of onset for lactose intolerance symptoms varies among carriers of associated alleles.
Convergent Evolution
Lactase persistence evolved separately in different regions through distinct genetic events and SNPs (single nucleotide polymorphisms – variations at a single nucleotide position in the DNA sequence). This indicates strong selective pressure (5,000 to 10,000 years ago) and shared cultural traits like animal domestication and adult milk consumption.
Co-evolution of Genes and Culture
Pastoral adaptation (animal raising) and adult milk consumption provide adaptive benefits (carbohydrates, fat, calcium, protein). However, lactose intolerance can cause drawbacks like diarrhea.
Some white nationalists use lactase persistence to justify racial purity. Human biologists criticize this claim because many populations beyond white people can digest milk.
Food Insecurity in America
Key Points from the Film “Hunger in America”:
- Food insecurity is defined as not knowing when your next meal will come.
- Approximately 50 million people in the US are affected by food insecurity.
- Those most affected include the middle class, “used-to’s”, single mothers, the elderly (with fixed incomes and limited resources), and the homeless.
- Major causes of food insecurity include unemployment, low wages, poverty, and inflation.
- Food insecurity is not defined by appearance.