Principles of Biochemistry Volume 3 - A. Lehninger 1985

Some aspects of human biochemistry
Human nutrition
Obesity results from the consumption of excessively calorie-dense foods

Obesity, which increases the likelihood of cardiovascular disease, Hypertension, and diabetes, occurs when the body's calorie intake exceeds its Energy Expenditure. Obesity typically develops in childhood or old age, and the longer it persists, the harder it is to overcome. The best way to combat obesity is by establishing sound dietary and exercise habits at an early age. Some people are more prone than others to convert calorie sources into fat, likely due to a reduced capacity for heat production resulting from a futile cycle (sect. 20.12) or the thermogenic action of brown adipose tissue (sect. 17.17). It is important to understand that obesity results from consuming excessive quantities not only of fats as such, but from an excess intake of calories in any form, whether fats, CARBOHYDRATES, or Proteins.

1 kg of human fat is roughly equivalent to 8750 kcal. Comparing this fact with the data presented in Table 26-3 allows us to estimate the degree of overeating that leads to a specific accumulation of excess weight. Gaining an extra 10 kg of fat in a 28-year-old man corresponds to an excessive intake of 10∙8750 = 87,500 kcal. Such fat accumulation can result from consuming an extra 150 kcal daily (which is only 5.6% of the average daily requirement of 2700 kcal) over 583 days, i.e., just over 18 months. Usually, however, excess weight accumulates over several years. Thus, in our example, if the accumulation of 10 extra kilograms of fat occurred over 5 years, it could be the result of consuming an excess 48 kcal per day, i.e., only 1.8% more than necessary. These data demonstrate how heavily body weight depends even on a minor increase (or decrease) in the number of calories consumed daily over prolonged periods.

Let us now consider how long it should take to reduce excess weight by lowering calorie intake. To lose 10 kg of fat, a person must consume no more than 2400 kcal/day for 42 weeks, or no more than 2100 kcal/day for 21 weeks, or 1800 kcal/day for 14 weeks. To lose weight even faster requires such a drastic reduction in the daily diet that it may lead to a decrease in physical performance. Rapidly losing ten extra kilograms of fat therefore requires almost heroic efforts. Table 26-9 shows the caloric content of certain foods that are frequently consumed in excess. The data in this table make it possible to determine which foods and to what extent daily intake must be reduced to achieve the desired rate of weight loss. Meanwhile, the data presented in Table 26-4 show what physical exercises must be performed to lose a specific amount of weight. The best way to maintain a constant body weight is to combine regular Physical Exercise with a consistent, balanced diet. It is substantially easier to prevent the accumulation of excess weight than to get rid of it afterward.

Crash diets create only an illusion of weight loss, as most of this loss is due to Water depletion from the body. In the long term, they usually prove ineffective because, in virtually all cases, people return to a calorie-excess diet afterward. Standard diets, which clearly specify the type and amount of food to be consumed daily, are convenient because they do not require calculating the caloric value of food using tables; however, they impose overly rigid restrictions on food choices over long periods, which can lead to deficiencies in certain Vitamins AND MINERALS.

Class="center">Table 26-9. Guide for controlling the caloric content of certain energy-dense foods