People assume that the ideal meal schedule spreads calorie intake over the course of the day: Never skip breakfast, keep your blood sugar on an even keel, and all that. But Mark Mattson, a neuroscientist at the National Institute on Aging in Baltimore, suspects that conventional wisdom may be due for an overhaul.
While many doctors encourage people to eat three square meals a day, there aren't data to indicate that it's important, he says.
In fact, says Mattson, "it may be healthy to have reduced meal frequency." In other words, skipping some meals–or occasionally fasting for the day–might be beneficial, even if overall calorie consumption remains unchanged.
Recent studies on lab animals seem to support that notion.
In one set of experiments, Mattson and his colleagues fed some mice on alternating days and forced them to fast on the days in between. They allowed other mice to eat daily. Both groups of animals were given unlimited access to food when they were permitted to eat. The mice that fasted intermittently gorged themselves when they could and so consumed as many calories on average–and gained as much weight during the 20-week study–as did their counterparts that ate daily.
Past studies have established that animals tend to age more slowly and live longer when they consistently consume fewer calories (SN: 11/25/00, p. 341: http://sciencenews.org/20001125/fob3.asp; 5/11/02, p. 291: http://sciencenews.org/20020511/fob2.asp). Researchers are still working to understand how calorie restriction slows aging, but they've observed that calorie-restricted animals have improved insulin sensitivity. In people, this change protects against diabetes.
Mattson and his colleagues observed better insulin sensitivity in the mice fed every other day than in those that ate daily.
"The [intermittently fed] mice are not calorie restricted, and yet we see changes in their physiology similar to those obtained with calorie restriction," Mattson told Science News Online.
Intermittent feeding also improved the animals' resistance to a neurotoxin that simulates Alzheimer's disease, the researchers report in the May 13 Proceedings of the National Academy of Sciences.
In another study, Mattson and two other researchers gave rats unlimited access to food either daily or every other day. They studied the animals' heart rate, blood pressure, and other physiological measures for 6 months.
To test the rats under stressful conditions, the researchers periodically restrained them physically or made them swim through cold water. The researchers then analyzed the rats' blood for several hormones that drive the body's response to stress.
When resting, rats fed only on alternating days had lower heart rates and blood pressure and less circulating glucose and insulin in their blood than did the other rats. The sometimes-fasting rats also showed muted cardiovascular responses to stress, suggesting that they more readily adapt physiologically to such situations.
The results of the hormone tests were less clear, but the researchers conclude that intermittent feeding helps the animals adjust to periodic exposures to certain stresses. The scientists didn't investigate whether temporary intermittent fasting had short-term effects on the animals' memory and learning ability. They report their findings in the June Journal of Nutrition.
"A meal-skipping diet . . . is good for cells throughout the body" because it periodically reduces the amount of glucose from digested food available to cells, says Mattson. During those times, cells build their ability to take up glucose when it's available he hypothesizes.
Thus, the mild stress of temporarily having less glucose may help cells prepare to cope with major stresses later, Mattson says. In that sense, meal skipping may be analogous to exercise in how it improves physiology. In fact, says Mattson, "intermittent fasting reduces blood pressure [and] reduces heart rate similar to what's seen with regular exercise."
Hard to swallow
Nutrition researchers find Mattson's hypothesis intriguing but a little hard to swallow.
Some past animal studies have found health benefits associated with restricted eating times, says Arlan Richardson of the University of Texas Health Sciences Center in San Antonio. However, they've also found that these animals eat fewer calories overall, which may explain the benefit.
If intermittent fasting turns out to improve longevity without calorie reduction, "that would be very exciting," says Richardson. But, he says, "I'd probably put dollars against it."
Mattson is quick to note that more research will be needed to determine whether his findings in animals also apply to people and whether they translate into long-term health gains. If they do, skipping meals–rather than going whole days without food–might be enough to derive some of the benefit, he says.
"I haven't eaten breakfast for the last 20 years, and I eat a pretty light lunch," Mattson says. If a person eases into the habit, "it's not that hard to maintain [after] a while."
The effects of temporary food deprivation may depend on the length of time over which calorie consumption averages out, Richardson comments. People who restrict their calorie intake for days or weeks at a time but overeat at other times–a practice commonly known as yo-yo dieting–suffer poorer health than they would if they constantly maintained the same average weight, he says.
Even if skipping meals carries potential benefits, behavioral aspects of eating may make the practice unhealthful. Some data indicate that people who skip meals as part of a weight-loss strategy actually end up consuming more calories because they binge at other times. In severe instances, this behavior can lead to the eating disorder bulimia.
Mark P. Mattson
Laboratory of Neurosciences
Gerontology Research Center
National Institute on Aging
5600 Nathan Shock Drive
Baltimore, MD 21224
Aging Research and Education Center
University of Texas Health Sciences Center
7703 Floyd Curl Drive
San Antonio, TX 78229