It’s mid-January: do you know where your New Year resolution went? You know the one about losing weight.
So maybe you are losing the weight you put on over the holidays? Maybe you are underway with a good weight loss program? Maybe you have already given up? No matter what your status, there is something you should know:
The human body is programmed to defend its weight and, when it senses weight loss, it starts cutting down its energy expenditure…big time!
Let’s talk about energy expenditure or “EE”. About 65-70% of calories burned each day are used to keep the routine body functions going, e.g. pumping blood, working the lungs, kidneys and liver. About 10% are used up in thermogenesis or the digestion of food. The rest, about 20%, is spent by the muscles in physical activity.
As far back as 1987, researchers compared the daily resting metabolic rate (RMR) of obese women who had lost weight and were no longer obese with women who were never obese. The researchers found that the post-obese women had metabolic rates approximately 15% lower than the never-obese group and they ate less.
So, metabolism in persons who have lost weight and those who are lean may not be the same.
Exercise and the heat value of food are skewed against those with obesity. In one experiment, 10 lean women and 10 women with moderate obesity were measured during periods of eating and exercise. Eating before exercise increased the exercise metabolic rate in lean women by 11% but only by 4% in women with obesity. The thermic effect of food was 2.54 times greater during exercise than at rest for the lean group, but only 1.01 greater for the women with obesity.
In a now classic 1995 paper by Jules Hirsch, Rudy Leibel and Michael Rosenbaum at Columbia University found that when a body loses weight, it adjusts by reducing its energy expenditure. This effect is so strong that an obese person who went from 250 lbs to 200 lbs would have to consume about 30% less than a 200 lbs person who had not lost weight just to maintain the same weight. This extra-reduction in food intake would have to continue indefinitely if the person were to maintain their weight loss.
This process, called by researchers “Adaptive Thermogenesis” can persist after active dieting for up to a year in one study. In an experiment involving subjects with severe obesity who were on a program of diet restriction and vigorous physical activity, researchers saw dramatic weight loss (over 30%) but a slowing of the resting metabolic rate (RMR) “out of proportion to the decrease in body mass, demonstrating a substantial metabolic adaption.”
Some researchers considered adaptive thermogenesis a major factor in the plateauing one sees in dieters, the increase in hunger and the eventual regain of lost weight. In one study of short-term severe diet and exercise subjects, the ‘metabolic compensation’ was seen as a major contributor to the less-than-expected weight loss. Individuals will have different adaptions to weight loss. In some cases, the effect can be significant. Tremblay et al state, “Indeed, as it is difficult to prescribe food intake that imposes an energy deficit exceeding 700-800 kcal per day to obese individuals, the decrease in energy expenditure in response to weight loss can entirely compensate for this prescribed deficit.”
Others are less sure. They seem to accept adaptive thermogenesis but see measurement problems and questions as to its utility in weight management.
The point is that our bodies contain a defensive mechanism against the disease of obesity. Until we realize that our strategies for prevention and treatment are like a novice chess player going up against a Grand Master. The point is: obesity is a lot tougher than our simplistic policy prescriptions assume.
The quandary of obesity has been expressed by Tremblay Chaput and Doucet in their article “Obesity: a disease or a biological adaption? An Update,“ Additionally, substantial body fat loss can complicate appetite control, decrease energy expenditure to a greater extent than predicted, increase the proneness to hypoglycaemia (low blood sugar) and its related risk towards depressive symptoms, increase the plasma and tissue levels of persistent organic pollutants that promote hormone disruption and metabolic complications, all of which are adaptations that can increase the risk of weight regain. In contrast, body fat gain generally provides the opposite adaptations, emphasizing that obesity may realistically be perceived as an a priori biological adaptation for most individuals. Accordingly, prevention and treatment strategies for obesity should ideally target the main drivers or root causes of body fat gain in order to be able to improve the health of the population.”