Small daily positive energy imbalances of 200 to 800 kJ (about 50 to 200 kcal) due to reduced resting energy expenditure (REE), reduced diet-induced thermogenesis, or physical inactivity are believed to predispose to obesity. However, estimates of the magnitude of the weight gain often fail to account for concurrent changes in body composition and increases in maintenance energy requirements as weight increases and energy equilibrium is re-established. Using previously reported data on body composition and REE in women and the energy cost of tissue deposition, we used mathematical models to predict the theoretical effect of a persistent reduction in energy expenditure on long-term weight gain, assuming no adaptation in energy intake. The analyses indicate the following effects of a reduced level of energy expenditure in lean and obese women: (i) REE rises more slowly with increasing degrees of obesity due to a declining proportion of the more metabolically active fat-free mass; so, for the same positive energy balance, a significantly greater weight gain is expected for obese than for lean women before energy equilibrium is re-established; (ii) due to the greater energy density of adipose tissue, the time course of weight gain to achieve energy balance is longer for obese subjects: in general, this is approximately five years for lean and ten years for obese women; (iii) the magnitude of weight gain of lean women in response to a reduced energy expenditure of 200 to 800 kJ/day is only about 3 to 15 kg, amounts insufficient to explain severe obesity.
"What counts is the cumulative effect! A new equilibrium is eventually reached after several months, or years depending upon several factors which include the magnitude of fat imbalance and initial body fat , the more excess fat in the body, the more time it will take to reach equilibrium and the more weight will be gained. Ultimately, the slow rise in whole body fat oxidation with time (accounted for by increased energy expenditure) will match the step rise in fat intake. "
[Show abstract][Hide abstract] ABSTRACT: Today, there are still uncertainties about the role of exogenous fat on body fat regulation. Early models of energy utilization (for example, Kleiber's, early 20th century) failed to take into account the nature of substrate oxidized in the control of food intake, whereas more recent models (e.g., Flatt's model, end of 20th century) did. Excess body fat storage is ultimately a problem of chronic positive energy balance mediated by a poor control of energy intake or/and a blunted total energy expenditure. Excess fat storage can stem from exogenous fat and to a more limited extent by nonfat substrates precursors transformed into body fat, mostly from carbohydrates, a process known as de novo lipogenesis. When considered over periods of weeks, months or years, total fat balance is closely related to energy balance. Over periods of days, the net change in fat balance is quantitatively limited as compared to the size of endogenous fat storage. The issues discussed in this article primarily include the stimulation of de novo lipogenesis after acute or prolonged CHO overfeeding and whether de novo lipogenesis is a risk factor for obesity development.
"Estimates of weight loss in response to food restriction go something like this: one pound of body fat contains about 3,500 kcal; a negative energy balance of 100 kcal per day would, thus, shed about 10 lbs in the first year and almost 100 lbs over ten years. The assumption is that the body's energy requirements remain steady as body size decreases, and that there is a fixed energy cost of 3,500 kcal/lb of lost tissue (Weinsier et al. 1993). "
"A greater fall in intake is necessary to maintain energy balance as we become physically more inactive. Weinsier et al. (1993) predicited (with elegant calculations) slow changes in weight over 5–20-year periods, so that the weight came up to a new plateau. This change occurs with average daily excesses of intake of only 420 kJ (100 kcal). "
[Show abstract][Hide abstract] ABSTRACT: A public-health approach considers the relevance of nutritional research in the prevention and management of obesity. Well-defined and internationally-agreed definitions based on BMI allow an assessment of the worldwide prevalence of overweight and obesity. There are about 250 million obese adults in the world, and many more overweight. Obesity is emerging in the Third World, first in urban middle-aged women. With economic developments, obesity then occurs in men and younger women. In the West childhood obesity is rapidly emerging, with concern that early-onset obesity is especially hazardous. In Asians the risks of excess visceral fat occur at lower body weights than in Caucasians. The propensity to visceral obesity in Asians may relate to malnourished mothers and low birth weight. The International Obesity Task Force is considering many issues, including the health economics of obesity. It has developed a strategy to define childhood obesity, which in children over 6 years is likely to predict long-term weight and health problems. While the search for genetic markers of obesity continues, with particular interest in the leptin gene, it is clear that societal change, with the decline in physical activity and the passive overconsumption of high-fat diets are major contributors to the global increase in obesity. The public-health aspects of obesity research are therefore challenging.
Proceedings of The Nutrition Society 06/1999; 58(2):385-93. DOI:10.1017/S0029665199000506 · 5.27 Impact Factor
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