The ‘eat-too-much, do-too-little’ theory of obesity claims that weight gain is caused by too much food and too little exercise. This we are told causes a positive energy balance that incrementally adds small amounts of adipose tissue. Over time the adipose tissue accumulation leads to the development of obesity. Proponents of this theory claim that the reversal of obesity pivots on the creation of a negative energy balance, that involves calorie restriction and increased physical activity. However, the scientific evidence is not supportive of such an idea. It is known that while there is an association between weight gain and exercise levels, the cause and effect of this relationship have been misinterpreted. In fact, a number of mechanisms are known that would prevent obese individuals exercising, which may suggest excessive weight gain is the cause of the lack of physical activity. In fact studies comparing third World populations with Western populations show greater body weights in the West, but no differences in physical activity.
Another problem for the proponents of the ‘eat-too-much, do-too-little’ theory of obesity is the inability of calorie restrictive diets to cause long term weight loss in overweight subjects. If eating too much is the cause of weight gain, it stands to reason that eating less would cause weight loss. However, results from clinical trials do not support the role of forced calorie restrictive diets in successful weight loss. In fact, such diets cause a loss of skeletal muscle mass, a decrease in resting metabolic rate and increased risk of subsequent weight regain in the form of increased adipose tissue stores. The fact that very low calorie diets cause long term losses of skeletal mass, but do not cause long term losses of adipose tissue in free living conditions, is therefore suggestive of factors being involved in weight gain and weight loss other than energy balance. However, another major problem for the proponents of the ‘eat-too-much, do-too-little’ theory of weight gain is that calorie intakes in Western populations may be decreasing.
For example, in a recent study published in the American Journal of Clinical Nutrition1, researchers analysed the energy intakes of a large cohort of the general population through data collected as part of the ongoing NHANE study (National Health And Nutrition Examination study). The study included data from almost 65,000 individuals and covered the years of 1971 to 2010. The results showed that the mean energy intake increased from 1955 to 2269 kcal per day from between the 1971 to 2004. However the mean energy intake decreased to 2195 kcal per day from 2004 until 2010. The authors concluded that this indicated a downward linear trend for energy intake since about 2004 in the United States. In subgroup analysis, the authors reported that while mean energy intakes peaked in 2004, for African Americans energy intakes peaked during the 2001-2002 period. In addition, while carbohydrate intake increased significantly from between 1971 to 2002, since this time carbohydrate intake has also decrease linearly.
This decrease in total energy and total carbohydrates is interesting nutritionally. In particular, a downward trend in total energy and total carbohydrates might suggest that obesity rates should begin to decline during this period. However, the opposite is true, as obesity rates are still climbing. This disparity is problematic for proponents of the ‘eat-too-much, do-too-little’ theory of weight gain, because according to the data, the increase in the rate of obesity should be slowing, or actually even falling. However, this is not the case. The decrease in total carbohydrates is also interesting, because nutritionally sugar is implicated in causing obesity. It is possible of course that while total carbohydrates are falling, complex starchy carbohydrate are being replaced by increased intakes of sugar. While on its own this data is not compelling, added to the other accumulating observations it suggest that factor other than total energy intake are responsible for weight gain, and therefore logically calorie restriction does not cause weight loss.
RdB
