Obesity threatens to become the foremost cause of chronic disease in the world and is increasing in incidence¹. Reasons for the increase include: urbanisation of the population, increased availability of food supplies, and reduction of physical activity¹.

Moderate obesity is undoubtedly multi-factorial in origin. Acquired influences probably exceed genetic factors in its causation¹. Appetite drive in humans is variable and could be under genetic control, as could be the regulation of energy expenditure, which could encourage obesity in sensitive individuals¹.

Obesity results from an imbalance between energy intake and energy expenditure². There is no conclusive evidence from epidemiological studies that under isoenergetic conditions dietary fat intake promotes the development of obesity more so than other macronutrients².

US dietary surveys indicate that the percentage of total nutrient energy consumed as fat has substantially decreased over the past two decades and this has corresponded with a massive increase in obesity³. There appears little doubt that a reduction in nutrient energy intake with aging is required to prevent age-related weight gain, but that weight gain cannot be prevented simply by substituting carbohydrates for fat¹.

Around 20-25% less calories per head per day is eaten than in the mid 1970’s (there may be biases in the data)⁴. The proportion of carbohydrate calories has declined and those of fat has increased, protein unchanged⁴. Research suggests that it’s the energy density of the diet that is important in determining interaction through physical activity⁴. Fat proportion, because it affects energy density, interacts with the level of physical activity to determine energy balance⁴.

Several reports note that the resting metabolic rate (RMR) declines with age, likely as a result of age-related reduction in muscle mass¹. If energy intake does not fall in parallel with loss of muscle mass, body fat will increase¹. Maintaining muscle mass through physical activity should receive a high public health priority as adults age¹ .

Reduced physical activity often starts in childhood¹ e.g.

The alarming increase in obesity in children and adolescents can be partly explained by these changes in society and culture, which is usually carried into adulthood¹.

Although much of the weight gain with aging is probably related to declining energy expenditure, food intake may actually increase after age 20¹. Once in a settled relationship, meals often become: more regular, frequent or generous in size, as eaten in restaurants or social gatherings¹.

A common pattern of response to increasing stress levels in adult life is to fall back on pleasurable escapes like eating, drinking and smoking. A common pattern in overweight, middle-aged adults includes periods of weight gain while under stress¹.

Personal and parental educational attainment and socio-economic status have been found to be significant predictors of higher levels of adult activity⁵. Women from social class 4 and 5 are also more likely to be obese⁴.

Research has suggested that a major controller of our daily food intake is the ability of our body to sense the presence of nutrients in the blood⁶. Perhaps, considering changes in micronutrient intakes alongside changes in macronutrient intake would be of merit?

1. Grundy S, Multifactorial causation of obesity: implications for prevention, Am J Clin Nutr 1998;67(suppl):563S-72S
2. Seidell, J, Dietary fat and obesity: an epidemologic perspective, Am J Clin Nutr 1998:67(suppl):546S-50S
3. Willett, W, Is dietary fat a major determinant of body fat?, Am J Clin Nutr 1998;67(suppl):556S-62S
4. Wiseman M, MSc lecture Surrey University 19/1/00, Principles of Applied Nutritional Science
5. Trends in Patterns of Disease and Diet
6. Koopmans et al (1991), Brain Res Bull 27:429-34