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Studies by Dr. Mark P. Mattson, chief of the National Institute on Aging's (NIA) Laboratory of Neurosciences, and colleagues have found that intermittent fasting and calorie restriction affect the progression of diseases similar to Huntington's disease, Parkinson's disease, and Alzheimer's disease in mice (PMID 11119686). In one study, rats and mice ate a low-calorie diet or were deprived of food for 24 hours every other day.[130] Both methods improved glucose metabolism, increased insulin sensitivity, and increased stress resistance. Researchers have long been aware that calorie restriction extends life span, but this study showed that improved glucose metabolism also protects neurons in experimental models of Parkinson's and stroke. Another NIA study found that intermittent fasting and calorie restriction delay the onset of Huntington's disease–like symptoms in mice and prolongs their lives.[131] Huntington's disease (HD), a genetic disorder, results from neuronal degeneration in the striatum. This neurodegeneration results in difficulties with movements that include walking, speaking, eating, and swallowing. People with Huntington's also exhibit an abnormal, diabetes-like metabolism that causes them to lose weight progressively. This NIA study compared adult HD mice who ate as much as they wanted with HD mice who were kept on an intermittent fasting diet during adulthood. HD mice possess the abnormal human gene huntingtin and exhibit clinical signs of the disease, including abnormal metabolism and neurodegeneration in the striatum. The mice on the fasting program developed clinical signs of the disease about 12 days later and lived 10–15% longer than the free-fed mice. The brains of the fasting mice also showed less degeneration. Those on the fasting program also regulated their glucose levels better and did not lose weight as quickly as the other mice. Researchers found that fasting mice had higher brain-derived neurotrophic factor (BDNF) levels. BDNF protects neurons and stimulates their growth. Fasting mice also had high levels of heat-shock protein-70 (Hsp70), which increases cellular resistance to stress. Another NIA study compared intermittent fasting with cutting caloric intake. Researchers let a control group of mice eat freely (ad libitum). Another group was fed 60% of the calories that the control group consumed. A third group was fasted for 24 hours, then permitted to free-feed. The fasting mice did not cut total calories at the beginning and end of the observation period, and only slightly cut calories in between. A fourth group was fed the average daily intake of the fasting mice every day. Both the fasting mice and those on a restricted diet had significantly lower blood sugar and insulin levels than the free-fed controls. Kainic acid, a toxin that damages neurons, was injected into the dorsal hippocampus of all mice. Hippocampal damage is associated with Alzheimer's. Interestingly, the scientists found less damage in the brains of the fasting mice than in those on a restricted diet, and most damage in mice with an unrestricted diet. But the control group that ate the average daily intake of the fasting mice (~10% restriction) also showed less damage than the mice on the restricted diet.[130] Another Mattson study[132] in which overweight adult asthmatics followed alternate day calorie restriction (ADCR) for eight weeks showed a marked improvement in oxidative stress, inflammation, and the severity of the disease. Evidence from the medical literature suggests that ADCR in the absence of weight loss prolongs life span in humans.[133] Intermittent fasting has also been shown to increase the resistance of neurons in the brain to excitotoxic stress.[130] |
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