U. ILLINOIS (US) — Obese dieters would do well to approach losing weight like the tortoise rather than the hare. Beginning a diet by fasting triggers alterations that work against shedding pounds.
“When obese persons reduce their food intake too drastically, their bodies appear to resist their weight loss efforts. They may have to work harder and go slower in order to outsmart their brain chemistry,” says Gregory G. Freund, professor of pathology at the University of Illinois. “Take smaller steps to start your weight loss and keep it going.”
For the study, published in the journal Obesity, Freund compared the effects of a short-term fast on two groups of mice. For 12 weeks, one group consumed a low-fat diet (10 percent fat); the other group was fed a high-fat (60 percent fat) and had become obese. The mice were then fasted for 24 hours. In that time, the leaner mice lost 18 percent of their body weight compared to 5 percent for the obese mice.
There is an immune component to weight loss that has not been recognized, Freund says.
“Our data show that fasting induces an anti-inflammatory effect on a lean animal’s neuroimmune system, and that effect is inhibited by a high-fat diet. Some of the brain-based chemical changes that occur in a lean animal simply don’t occur in an obese animal.”
The breakdown occurs because obese animals resist downregulation of genes that activate the interleukin-1 (IL-1) system and associated anti-inflammatory cytokines.
Freund also studied differences in the behavior of the two groups of mice, monitoring how much they moved, administering tests to discern the animals’ ability to learn and remember, and noting whether they exhibited signs of depression or anxiety.
The results suggest that starting a diet with a fast or near-fast may alter brain chemistry in a way that adversely affects mood and motivation, undermining the person’s weight-loss efforts.
Also, beginning a weight-loss program in a depressed frame of mind and with decreased motivation doesn’t bode well for the diet’s success, Freund says.
“The obese mice simply didn’t move as much as the other mice. Not only was there reduced locomotion generally, they didn’t burrow in the way that mice normally do, and that’s associated with depression and anxiety.”
Funding was provided by the National Institutes of Health.
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