Causes of Obesity – Nurture versus Nature

Nurture Theories Eating to satisfy : Eating to satisfy : Boredom Boredom Parents Parents Stress Stress Culture Culture Effect of age Effect of age Ego Ego Å Most obese adults were slim when young Obesity may be caused by phycology

Nature Theories = Obesity caused by physiology Dieting does not help Ageing Muscle tone Diet induced Thermogenesis Diet induced Thermogenesis Glycogen storage variations Glycogen storage variations Need large food intake to maintain Nitrogen Balance

Benefits of Obesity = Obese people do not get osteoporosis = Obese people do not get osteoporosis. This may be due to their higher insulin secretion reducing calcium lost in the urine.

Why Dieting Doesn't Work = Reduced energy intake causes the body to adapt:  lowers “basal metabolism ” ; burns up fat ; reduces energy using tissue – lean body mass ; When you go off the diet Å use less energy Å get fatter than before

Transport of Lipids in Blood = Lipids are insoluble in water and blood fluids – must be carried with proteins called Lipoproteins

Lipoproteins = Chylomicra carry fat from Intestine to tissue = LDL ( low density lipoprotein) ¥ carry lipids from Liver to tissues ¥ VLDLP loose fatty acids to tissues they get denser and become IDLP and eventually LDLP then Reminant LDLP and chylomicra return to liver = HDL carry cholesterol from tissues to liver – known as Revers transport

Lipoproteins Chylomicra Intestine Liver Body tissues VLDLP HDLP LDLP IDLP

Danger of Excess Dietary Fat - = Cancer = Undigested fatty acids reaching the colon stimulates cancer = fatty acids make soap that wash of cells off the lining the gut = This acts as a MITOGEN ie stimulates cell growth = Cancer needs two stages to start: Mutagen and then mitagen

Danger of Excess Dietary Fat = Increases cholesterol production – imbalance of carbohydrate and fat metabolism – cardiovascular disease = Obesity = Diabetes Cardiovascular Disease

Normal Catabolism

High Fat Catabolism

Fat Carbohydrate Imbalance = More fat means less carbohydrate = Less anaplerosis => more cholesterol = Not all fat the same ??? = Unsaturated seam OK = Long chain fatty acids seam OK = Short chain fatty acids reduce CVD = Medium length FA seam worst

Danger of Excess Dietary Fat = Increases cholesterol production – imbalance of carbohydrate and fat metabolism – cardiovascular disease = Obesity = Diabetes Cardiovascular Disease

Normal Catabolism

High Fat Catabolism

Fat Carbohydrate Imbalance = More fat means less carbohydrate = Less anaplerosis => more cholesterol = Not all fat the same ??? = Unsaturated seam OK = Long chain fatty acids seam OK = Short chain fatty acids reduce CVD = Medium length FA seam worst