Many people believe that fat loss is only possible with forced calorie restriction. This is so ingrained in the psyche of the mainstream arena that to question the idea results in an incredulous response. That forced calorie restriction does not cause long-term weight loss is well documented in the scientific literature, mainly through the high failure rates of such regimens. In addition, studies show that periods of forced calorie restriction may cause permanent deleterious effects that substantially decrease the chance of future fat loss. The reason that forced calorie restriction does not cause long-term fat loss is because it does not address the underlying cause of obesity. That is a low quality Western style diet that contains carbohydrates with a low fibre to starch ratio, as well as high intakes of fructose containing sugars. These refined diets cause insulin resistance and metabolic dysfunction which can only be reversed through removal of the underlying cause.
That some short-term fat loss occurs on forced calorie restriction diets is not contentious and is well reported in the literature. For example, in a study published in the American Journal of Clinical Nutrition1, subjects fed a 420 kcal per day very low calorie liquid diet lost 20.5 kg over a period of between 13 and 22 weeks. However, fat accounted for only 83% of the lost weight, which meant that the mean loss of lean mass was 3.5 kg. This is problematic because this loss is likely to comprise almost exclusively of skeletal muscle which is responsible for the majority of the resting energy needs. The reduction in lean mass therefore causes a reduction in the requirement for energy, which makes further weight loss unlikely, and future weight regain almost inevitable if an ad libitum low quality Western diet is resumed. Therefore, while overweight individuals tend to have higher resting metabolic rates (RMR) compared to lean counterparts, following weight loss their RMR is deleteriously lowered.
The damage to resting metabolism caused by dietary induced loss of skeletal muscle was illustrated in another study published by the same authors in the same journal2. Healthy women 126 % over of their ideal body weight were placed on a 420 kcal per day very low calorie liquid diet which caused a weight loss of 1.1 kg per week (mean total loss 19.9 kg) until a predetermined weight was achieved. At this point the researchers measured their thyroid function and RMR to determine if the weight loss had caused a decrease in their resting requirement for energy. Following weight loss, RMR decreased significantly. In addition there was a significant decrease in triiodothyronine (T3) and reverse T3, due to a decrease in the metabolising enzymes that convert thyroxine (T4) to T3 (as pointed out by Dan Duchaine in Body Opus). During the 5 week re-feeding period, T3 and RMR increased, but did not return to baseline levels.
As the subjects were reintroduced to a solid food intake of 800 kcal per day, the researchers were ‘surprised’ that further weight loss did not occur. The fact is that many people are so brainwashed into thinking that weight loss must occur if calories are restricted that they dismiss the accumulated evidence that shows otherwise. In the case of the study authors, the lack of further weight loss on the 800 kcal per day diet was put down to ‘cheating’ by the subjects. Of course, the study authors were too biased to accept the data at face value and ascribe an alternative explanation to explain the findings. The fact is that obesity is a serious metabolic abnormality caused by insulin resistance, that results in hypothalamic insensitivity to the hormone leptin. Leptin resistance in the hypothalamus initiates physiological resistance to weight loss because of the perceived presence of a starvation state. Only removal of the metabolic disturbance that causes leptin resistance can cause successful fat loss.
RdB
