Body Mass Regulatory Mechanism Versus Obesity and Weight Loss
The nonhomeostatic control of feeding and the operation of hedonic neural substrates that facilitate food intake despite supranormal body fat accumulation instruct us that the prerequisites for maintaining healthy body mass level are restraint in eating food, high levels of physical activity, and periodic episodes of weight loss. The obstacles to using this strategy for facilitating weight loss once obesity has developed include a powerful hunger drive, reduced motivation to be physically active, and physiological adaptations that counteract body mass loss and make weight regain highly efficient. A meta-analysis of the effectiveness of different approaches to weight reduction in obese humans shows both a gradation of effects depending on the method of energy restriction and clear evidence for a defense of predeprivation weight (figure 6.12; Franz et al., 2007).
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To optimally engage our presumed Paleolithic mechanism of regulating body mass, we would need an exercise energy expenditure of about 500 kcal/d (Eaton & Eaton, 2003), higher muscle mass relative to adipose tissue at sex-appropriate ratios of 50% muscle:10% fat in men and 45% muscle:15% fat in women, and a BMI of about 21 kg/m2 (Eaton et al., 2009). This would require a rigorous regime of endurance and strength training because such physique is approached only in professional athletes. A change in muscle:fat ratio would increase the proportion of IRs on muscle relative to adipose tissue and thus significantly increase glucose tolerance and insulin action. We also may need to engage in cycles of fasting and feasting and periodic episodes of body mass reduction to optimally activate insulin sensitivity and the operation of our thrifty metabolic proteome (figure 6.10). A drastic change in our diet would also be required (Eaton, 2006). The Paleolithic diet consisted of about 35% fat, 35% carbohydrate, and 30% protein. Polyunsaturated fats predominated, 50% of carbohydrate was derived from uncultivated plants and contained only 2 to 3% sugars from honey, and almost no grains and dairy products were included. Fiber consumption was about 100 g/d, and vitamin intake was between 2 to 8 times higher than vitamin intake in the contemporary diet. Clearly, attainment of such a goal would require a drastic re-engineering of our current lifestyle. The optimal way to approximate this goal would possibly be to prevent the development of obesity by restraining food intake and significantly increasing levels of physical activity. Absent this option, an obese person could reduce body mass through exercise and dieting and then successfully maintain reduced body mass by restricting food intake to about 1400 kcal/d and by spending about 1 h in physical activity each day (Epstein & Wing, 1980; McGuire et al., 1998; Wing & Phelan, 2005). Success of this strategy has been documented by the research by National Weight Control Registry, spearheaded by Dr. Rena Wing. Considerable obstacles to the implementation of this strategy are the disparity between the hedonic allure and ease of consuming palatable, energy-dense, and easily accessible food and the amount of physical effort required to expend the calories so obtained and the challenge of incorporating sufficient levels of physical activity into our largely sedentary contemporary lifestyle.
