Williamson Obesity Flashcards
How is obesity generally defined?
Using BMI (body mass index = weight in kg / height in m).
What is obesity a consequence of?
Consuming more energy intake than your body needs through either too much food or too little exercise.
What are the main food categories?
Carbohydrates (sugars), fats, proteins, and fibre. We also need minerals and vitamins. Fibre is indigestible food material, mainly plant cellulose. No nutritive value – bulks up food and helps digestion and excretion.
What are characteristics of carbohydrates?
Historically, low fraction of European diet. Meat and fish have little. Fruit contains fructose and some sucrose. Milk contains lactose. Fruit and vegetables contain starch – harder to digest so released more slowly. Plant material contains lots of cellulose and hemicelluloses – not digested by humans. Main intake now is sweet food and sugary drinks – high content of refined sucrose.
What are characterisitcs in fats?
In meat and fish; and in seeds, hence vegetable oil etc. Many of the flavours we know and love are soluble in fat not water, so without fat, food has little taste. Fat also includes cholesterol.
In animals (and in humans) the main fat is triglycerides, and is stored in adipose tissue.
How do higher organisms store energy?
Animals store most of their energy reserves as fat. Plants store it as carbohydrates (starch). Not least because the energy content per gram is much greater in fats – so less weight to carry if it is fat. Plants don’t need to move! Sugars are water-soluble but fats aren’t, so sugars are much simpler to use.
How is protein catabolised?
Protein in food is needed for making protein. Needs breaking down to monomers, plus some recycling, and then build back up into protein. Stomach and gut contain a variety of enzymes to break proteins into amino acids and short peptides. Then transported into body: circulate in blood, and take up in tissue and liver.
How is fat catabolised?
Complicated because insoluble. Triacylglycerides in diet emulsified by bile salts, broken down by lipases and transported into mucus cells. Then reassembled into triacylglycerides and packaged into apolipoprotein-bound chylomicrons. The shorter chain fatty acids ( C14, more common in dairy products) do not need esterifying and are transported as free fatty acids (in chylomicrons etc).
How are lipids moved around the body?
Lipids pass into lymph system and then into the blood. When they reach target cells, they are broken down again. Subsequently either attached to CoA for -oxidation, or re-esterified for storage. Liver can oxidise fatty acids to ketone bodies which are soluble 4-carbon molecules and used eg by muscle.
How is sugar catabolised?
Body has very tightly controlled system for maintaining blood glucose constant, around 5 mM. Sugars in diet are broken down to monosaccharides in the gut, transported into epithelial gut cells, and then into blood. In the liver, different sugars are rapidly converted to glucose. Sugars taken up in diet are stored as glycogen (until no more space, and as long as insulin does its job). Prolonged excess glucose in diet messes up insulin control = type 2 diabetes. Excess sugars (ie peak in blood sugar or glycogen stores full) are converted to fat, via acetyl CoA.
What is the thrift gene hypothesis?
Short-term build-up of fat is good – but chronic nutritional excess is bad (positive selection for glucose and lipid metabolism genes – discussed in Bouchard 2007).
What energy sources do slow muscle fibres use?
In ‘slow’ muscle (non-skeletal muscle eg blood vessel contraction), most energy needs are met by conversion of glucose to pyruvate. This provides very little energy, but the advantage is that pyruvate is converted to lactate in muscle which is then recycled to the liver where it is converted back to glucose.
What energy sources does skeletal muscle use?
Skeletal muscle can use glucose or free fatty acids, or ketone bodies. ‘Fast twitch’ muscle almost entirely glucose from glycogen, because faster.
What tissues can only use glucose as an energy source?
One is red blood cells – no nucleus, no mitochondria, very little metabolism except glycolytic pathway. The other is the brain. If blood glucose drops below about 3 mM, the brain stops working and you go into a coma. (Brain can also use ketone bodies, though glucose is preferred.)
What happens to energy sources under starvation?
Fat can be converted to acetyl CoA and turned into ketone bodies which can keep most processes going. Except the brain, which needs some glucose – supplied by breaking down protein – very much a last resort as protein is never intended as an energy store. Breakdown of triacylglycerides also provides glycerol which can be converted to glucose
