Dear Age Smart: Does Fasting Slow Aging? From a person who loves to feast.
Dear Feaster: Does fasting slow aging? Surprisingly, that might be true. But it depends what you mean by “fasting”. Prolonged fasting can obviously lead to malnutrition and early death. On the other hand, there is evidence that intermittent, brief fasting may have significant health effects in people whose overall health could tolerate 16 to 24 hours with little or no food (but ample fluids!). Google “intermittent fasting” and you’ll find dozens of websites and blogs that taut health benefits from periodic calorie deprivation. Dr. Andrew Weil’s Huffington Post column from August 6, 2012, provides a nice summary of the rationale for intermittent fasting and some of the benefits seen in animal and human studies. Dan Buettner, creator of the famous “Blue Zone” books and “Blue Zone Project” that promotes healthy lifestyles for long life, recommends going 16 hours a day (or night) without food. He confines his caloric intake to two meals a day over an 8 hour period of time (a large morning meal and a smaller one early evening). And there actually is a lot of compelling research in animal models of human disease that supports health effects of fasting. There are fewer studies in humans, but so far, the data suggest that fasting has health benefits in people as well.
Many of these published studies rely on alternate-day fasting paradigms, in which experimental animals and people are given more than their usual amount of food one day (175% or “feasting”), and less the next (25% or “fasting”). That adds up to normal caloric intake over two days, so no weight loss occurs. Yet, blood sugar (glucose) levels drop, insulin levels drop, growth hormone levels rise (less fat, more muscle), blood markers of oxidative stress decrease and brain neurotrophic factors increase. Brain hippocampal cells (where memories are first formed) become more resistant to neurotoxins. During fasts lasting more than 12 hours, the body begins to burn molecules derived from fat (ketones) rather than glucose, which can have certain benefits for brain function. While it has long been thought that eating 30-40% less every day prolongs life in animal models of human disease, the evidence to date is that intermittent fasting provide similar benefit (see Varady and Hallerstein’s review in American Journal of Clinical Nutrition from 2007). If you adopt the every other day fast, I wouldn’t recommend eating 175% on the “feasting day” though; that seems like too much food for one day. And if you want to lose weight, you will if you only eat a little more than usual on the days you eat, since overall caloric intake will be less.
Dr. Mark Mattson of the National Institute on Aging argues that intermittent fasting mimics the feast or famine conditions under which our “hunter-gatherer” ancestors evolved. Before grocery stores, food supplies came and went with the success of the hunt or harvest. In some parts of the world, many people still live “off the land” and some of them are the longest-living populations. Our bodies are primed to take advantage of food when it is available and to do “repair work”, increase cellular resistance and use energy efficiently when it is less available. This makes sense, although I’m not certain that evolutionary strategies for people who were old at 40, necessarily apply to people who routinely live twice that long. We’re in it for the long haul now, but one has to acknowledge the scientific evidence for this ancient way of eating demands attention.
Of course, beyond the waxing and waning of food supplies, people have been fasting for centuries for religious and spiritual reasons. The origins of these rituals may be based on the spiritual focus that physical deprivation can bring, but our ancestors surely noticed the renewed energy and clarity of mind that can result from brief fasts and attributed this to divine connection. I fast one day a year for a religious holiday and find that I have great energy at the end of that day (although I am plenty excited about the evening breakfast meal). Based on that experience and the science behind fasting, I’ve been experimenting with a light, earlier dinner (supper) and a late morning breakfast. This 14 to 16 hour overnight fast seems to be easier to for most people than alternate day fasting. At the very least, it means going to bed with a lighter stomach, which provides several immediate benefits, especially for people with gastric reflux.
Here are some important caveats: Although there are compelling data for potential benefits, the claims for fasting reducing risk for diseases such as diabetes, cancer, heart disease and neurodegenerative diseases (such as Parkinson’s and Alzheimer’s diseases) that you see on the internet are premature in my opinion. But going brief periods of time with less food (but again, plenty of water!) seems reasonable so long as you’re not a person who shouldn’t fast at all. Women who are pregnant or breastfeeding shouldn’t fast. People with diabetes who are on medication, especially insulin, shouldn’t fast. People with eating disorders, renal or liver disease should not go long without eating. And let’s be clear, we’re not talking about fasting for weight loss. That doesn’t work for long. You’ll lose weight all right, but it won’t stay off. Fasting for more than one day at a time stresses the body in ways that can counteract the benefits. Fasting is not a weight loss strategy. You will lose weight with a prolonged fast, but your metabolic rate slows, you lose muscle and brain and you will regain weight quickly once the fast ends. But with an every other day fast regimen or an overnight 16 hour fast, you likely will lose some weight slowly and maintain a leaner body, just so long as you don’t overeat when the fast ends.
Fasting may not be a good idea if you’re doing physically demanding work or exercise; you’ll also need to eat to replenish your glycogen supplies for immediate energy. And don’t neglect the quality of your nutrition. You’ll want to avoid high sugar content foods on any day, especially if you take light snacks on your fasting day. If you’re thinking of incorporating intermittent fasting into your routine, I’d recommend speaking with your health care provider or a registered dietician before undertaking any kind of fasting regimen long term.