Saturday, November 30, 2013

Alternate day fasting: healthy and good for weight-loss?

Diet fads tend to come and go, and few of them ever have a sound scientific basis, which is one reason why they don't last. Sooner or later, unanticipated side effects often crop up, including fatigue, muscle loss, and even failure to lose body fat. A recent diet trend that has been making its way around the Internet is alternative day or intermittent fasting.As the name implies, this involves eating normally one day, followed by eating far less the next. The fasting day doesn't involve complete avoidance of food and drink, but rather consuming an average of 25 percent of normal daily caloric intake.
   The notion that eating less improves health and fosters longer life is the cornerstone of the classic caloric restriction diet. With this diet, you consume 30% less calories then your normal intake every day. Animal studies show that eating in this manner is the only established way to maximize life span. One recent study involving monkeys, however, showed no actual life extension benefits from CR. Other primate studies have shown slowed aging effects, such as low insulin and glucose, lack of insulin resistance, along with lower rates of various diseases, such as diabetes, cardiovascular disease, cancer, and cognitive disease, such as Alzheimer's disease.
   But the truth is that there is no actual human evidence that CR styles of eating can extend human life. There are people who eat in this manner based on the findings of benefits in animals. Such people do tend to show lower resting insulin, blood pressure, lipids and so on. But they are also painfully thin, with a catabolic appearance suggesting a loss of muscle mass. They are also often frequently cold and tired. Clearly, there must be a better way.
    Animal studies that compared intermittent fasting with the standard daily CR regime, found that the animals lived just as long when following the IF plan as when eating the far more restrictive CR style. Indeed, in some ways the IF animals were healthier, showing lower resting insulin and glucose levels compared to their CR peers. Other animal studies, usually involving rats and mice, show that IF exerts protection against strokes, and slows cognitive loss or brain function deficits. IF also boosts the levels of chaperon proteins, which repair misfolded proteins in the body that are linked to various diseases, including Alzheimer's. IF appears to increase the level of brain-derived neurotrophic factor, which is involved in neuron repair, by 50 to 400%.   Autophagy is a process by which old cells are broken down to allow room for new cells. When this process is impaired, aging ensues. IF is known to boost autophagy.
    Of course, eating less would also promote loss of excess body fat, as well as increased insulin sensitivity. In one mouse study, the mice were permitted to eat unrestricted amounts of high fat foods for 8 hours, followed by not eating for the next 8 hours. Despite the initial overeating,none of the mice got fat or showed elevated insulin levels. Studies of humans who followed short-term IF regimes showed moderate fat loss, but a significant improvement in several health values, such as increased HDL cholesterol, lower triglycerides, lower insulin and so on.
   The latest human study on IF involved 32 subjects randomly selected for either a IF group, or a control group for 12 weeks. The IF group ate normally one day, followed by eating 25% of their normal intake the next day. The subjects in this study included both normal weight and overweight people. The results after 12 weeks showed an average 6% weight loss. But more significantly, several health benefits were also evident. These included lower blood triglycerides, lower CRP (a measure of inflammation), lower leptin (lower hunger), and an increase in LDL particle size, which is associated with a decreased risk of cardiovascular disease. Levels of adiponectin, linked to increased insulin sensitivity, also rose in the IF group. The adherence to the IF diet was high, although the subjects did confess to moderate hunger on the fasting days. Most impressive, however, was that none of the fasting subjects loss any lean mass or muscle. That is an important consideration, since loss of lean mass is a common side effect of most diet plans, and is the main cause of weight regain after such diets.
     It appears that, if you can handle it, following a IF regime may help you lose some body fat quickly, without losing muscle. As for using the IF plan continuously, this is possible, but the long-term effects are as yet, not known. I suspect that one notable advantage of IF over CR regimes is that with CR regimes, you experience a significant drop in all anabolic hormones, including testosterone, growth hormone, and IGF-1. With IF, because you are still eating normal amounts of food every other day, these hormones are maintained, so no muscle loss ensues. In addition, you get all the benefits of the CR without the constant starvation. One note of caution, however: in rats who followed long-term IF regimes, their hearts showed a stiffening effect that could result in future congestive heart failure.

Varady, KA, et al. Alternate day fasting for weight loss in normal weight and overweight subjects: a randomized controlled trial. Nutrition Journal 2013; in press.

©,2013 Jerry Brainum. Any reprinting in any type of media, including electronic and foreign is expressly prohibited.

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