Human Nutrition (D1)

• Essential nutrients cannot be synthesised by the body, ∴ they have to be included in diet. A nutrient is a chemical substance found in foods that is used in the human body. Dietary minerals are essential chemical elements (eg: Na, Mg, Ca & K). Conditionally essential nutrients are produced when the precursor is present (eg: tyrosine [conditionally essential amino acid]). 
• Phenylketonuria: (PKU)


  Genetic disease caused by mutations of a gene coding for the enzyme that converts phenylalanine into tyrosine. Mutations produce alleles of a gene that codes for enzymes unable to catalyse the conversion rxn. Phenylalanine then accumulates in body → deficiency in tyrosine. PKU can → high phenylalanine levels which → ↓ growth of head & brain, w mental retardation of young children & severe learning disabilities. Only 1 normal allele is needed for satisfactory conversion of phenylalanine to tyrosine, ∴ PKU is a homozygous recessive disease. 
• Treatment for PKU:

  Involves eating a diet low in phenylalanine for the rest of the person’s life (meat, fish, nuts, cheese, peas & beans can only be eaten in small quantities) Tyrosine supplements may be needed.
• Many organic C compounds are considered essential. Vitamins are chemically diverse C compounds that the body cannot synthesize. Some fatty acids & amino acids are essential (eg: omega-3 fatty acids). Lack of essential amino acids affects prod of proteins → malnutrition.
• Diets based on tropical crops cassava (a root crop)/ plantain (a type of banana)/ sweet potato are eg of diets low in protein. Protein deficient malnutrition can → lack of blood plasma proteins → fluid retained in tissues, which can cause swelling, aka ‘edema’, ≈ seen in the abdomen. When children experience prolonged, extreme protein deficiency, their mental & physical development suffers. Clinical symptoms of protein deficiency are evident in patients with conditions aka kwashiorkor & marasmus.
• Vitamin C deficiency signs are:

  • Scurvy 
  • Haemorrhages occur under skin & other tissues, gums become swollen & spongy, and teeth loosen & fall out. 
  • ↑ susceptibility of the mouth & gums to infection 
  • ↓ in the rate at which wounds & tissue dmg heals
• Until 1907, scurvy was thought to be specific to humans, cus attempts to induce symptoms in lab rats & mice were entirely unsuccessful. Then it was discovered that the guinea pig was another animal that could not manufacture ascorbic acid. Guinea pigs, fed on diets free of this vitamin & displayed symptoms of the disease &, by using this animal model, it proved that scurvy was a disease due to deficiency of vitamin C & that it wasn’t a disease specific to humans. The chemical, ascorbic acid, was isolated & named in 1932. Scurvy was first recorded in 1545.
• Malnutrition may be caused by a deficiency/ imbalance/ excess of nutrients in the diet. 
• Eg of malnutrition caused by excess include:

  • Obesity (Excess energy, fats & carbohydrates)
  • Type II diabetes
  • Hypertension
  • Coronary heart disease
• Eg of malnutrition caused by deficiency include:

  • Kwashiorkor & marasmus (Protein)
  • Scurvy (Vitamin C)
  • Rickets & osteomalacia (Vitamin D)
• Vitamin D is concerned w absorption of Ca & P by the body. Lack of vitamin D/ Ca can affect bone mineralization. Infants deficient in vitamin D/ Ca develop rickets & have deformed bones, ≈ too weak to support them. In the elderly, deficiency in vitamin D/ Ca → osteomalacia, in which bones soften.
• Anorexia means ↓ appetite. Anorexia nervosa is a psychiatric illness, w causes that are complex. Both involve voluntary starvation & loss of body mass. Amt of carbohydrate & fat consumed is too small to satisfy the body’s E requirements, so protein & other chemicals in the body are broken down. As body weight in a person w anorexia ↓, skeletal muscle is digested & heart muscle deteriorates. Both skeletal muscle & cardiac muscle do not contract normally under these circumstances. There is ≈ ↓ blood pressure, ↓ heart rate & ↓ heart output in patients.
• Studies by WHO estimate that 1 billion ppl are overweight & 300 million are obese worldwide. In a developed country like the UK: 13–17% of men & 16–19% of women are clinically obese. Overweight indi ≈ suffer hypertension & type II diabetes.
• In type II diabetes, β cells of the islets of Langerhans in pancreas ≈ produce insulin in sufficient qtys, but when obese, insulin receptors on target cells are less sensitive. The patient has a generally ↑ blood glucose level.
• Hypertension is a condition of persistently raised blood pressure. Blood pressure = pressure of the blood flowing through the arteries. Blood pressure is quoted as 2 values, 120 & 70 – 80 mmHg.
• Research has shown correlation btw high levels of cholesterol in blood plasma & ↑ risk of coronary heart disease. Cholesterol consists of low-density lipoprotein (LDL) & high-density lipoprotein (HDL). Excess LDL is deposited under the endothelium of artery walls, beginning/ enhancing plaque formations. HDL ↑ efficiency of the receptor sites for the removal of bad cholesterol from the blood.
• In the brain's hypothalamus, there is a centre responsible for making us feel satisfied when we eat enough food. It aka appetite control centre. Hormone leptin suppresses the sensation of hunger upon reaching the appetite centre. When fat cells fill up, they secrete more leptin. When fat cells empty & shrink, they secrete ↓ leptin & sensation of hunger is exp in brain.
• Parabiosis mice experiment showed that ob gene produced leptin while db gene produced leptin receptor. The db mice had normal leptin production but mutant leptin receptor. It produced leptin constantly & the wild type mice died of starvation!