PHYSIOLOGICAL ADJUSTMENT AND MAINTENANCE OF FAT LOSS
Summary of main points.
• Plateaus in fat loss arc common and are due to physiological adjustments and reversion towards old habits.
• Maintenance of fat loss can be extremely difficult due to changes in metabolic rate and body composition.
• Physiological adjustments result in a lower than predicted loss of body fiat with changes in energy balance.
• Adaptations include decreases in metabolic rate, changes in body composition, changes in fat utilisation and modifications of food intake.
• Plateaus may be countered by change.
As most perennial dieters will tell you, it’s easy to lose fat, but keeping it off is another matter. If fat losses continued in direct proportion to the initial energy deficit (i.e. energy in minus energy out, as proposed in earlier models of fat loss), there would be a steady decline towards a goal given a constant deficit in energy balance, but this is seldom the case. There is an initial significant loss, then the rate of decline decreases until a type of ‘plateauing’ occurs followed often by a return to baseline levels. The challenge is to determine why this is so and if and how this can be modified.
Undoubtedly part of the reason for plateaus and regain is a return to previous habits. People tend to start fat loss programs with great gusto and commitment, but after 3 to 6 months their exercise and dietary habits tend to start slipping back. This is common and understandable given the environment of high-fat foods and labour-saving devices they face. To swim against this environmental ride takes effort and the effort is greater for those more genetically predisposed to obesity. It is not surprising that the effort fades with time. People often find it difficult to admit to a return to old habits and seek metabolic explanations for their plateaus. In truth, for most people the plateaus are due to a combination of behavioural and metabolic factors.
The extent to which metabolic changes slow down fat loss is a matter of some considerable debate. In 1950, the US nutritionist Dr Ancel Keys, wrote: It might seem entirely reasonable that the energetic processes of the body diminish in intensity as the exogenous food supply is reduced. It is reasonable in the sense that a wise man reduces his expenditure when his income is cut.’ This survival tactic has been well-described in animal models of obesity. Studies at Cambridge University on a particular species of desert mouse for example, have shown that when compared with a ‘dry mouse—or one accustomed to plenty of food—the desert mouse is able to adapt to decreases in body weight caused by lack of sustenance by simply slowing down its metabolic processes. Humans have less facility to actively alter metabolic processes to match changes in food intake, although adaptations do certainly occur.
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