Nature is all about booms and busts - it is common for species to grow too large to be sustainable. Humans were once that way too, but science has now made it possible for even the poorest people to be fat. We no longer have a feast or famine existence.

And the worst thing you can do to lose weight is go on a 'crash' diet, according to modern nutritional thinking - your body quickly goes into starvation mode. But that is in the short term, clearly if you were to go on a starvation diet for any extended period, you lose a lot of weight, it happens every season on "Survivor".  Mitochondria, the little energy factories in our cells, are nimble about optimizing what they have and do not have.

Those jolts to metabolism may even increase longevity - unless you take antioxidants while fasting, finds a new study. Free radicals get a bit of a bad rap, they are clearly also our biological friends as long as they don't get out of control and damage cells in the food oxidation process, and a feast or famine diet that mimics fasting is helpful, but antioxidants that help us on a normal diet could get in the way while fasting.

If they are weaned on that kind of starvation diet, fasting has been shown in mice to extend lifespan and to improve age-related diseases. But fasting every day, which could entail skipping meals or simply reducing overall caloric intake, can be hard to maintain. Reducing calories is obvious enough, every study shows that the only way to lose weight is to burn more calories than we consume, but fasting has become a no-no to modern nutritionists, which might explain why more people on a diet than ever and more people never lose weight: Everyone thinks there is an easy path where they eat six times a day.

No one wants to make money and watch television commercials about eating and not eat, but intermittent fasting could work, if you can take it. The stomach retrains itself rather quickly so for the first 24 hours you would have rumblings of hunger but after that you would not, and your energy levels would be high again. But unless you can do it for three or four days at a time, the annoyance of feeling 'hungry' for 24 hours would be no good for people.

Michael Guo, M.D., a Ph.D. student in genetics at Harvard Medical School, said the team group measured the participants' changes in weight, blood pressure, heart rate, glucose levels, cholesterol, markers of inflammation and genes involved in protective cell responses over 10 weeks. "We found that intermittent fasting caused a slight increase to SIRT 3, a well-known gene that promotes longevity and is involved in protective cell responses." 

The SIRT3 gene encodes a protein also called SIRT3. The protein SIRT3 belongs to a class of proteins called sirtuins. Sirtuins, if increased in mice, can extend their lifespans, Guo said. Researchers think proteins such as SIRT3 are activated by oxidative stress, which is triggered when there are more free radicals produced in the body than the body can neutralize with antioxidants. However, small levels of free radicals can be beneficial: When the body undergoes stress -- which happens during fasting -- small levels of oxidative stress can trigger protective pathways, Guo said.

The group recruited 24 study participants in the double-blinded, randomized clinical trial. During a three-week period, the participants alternated one day of eating 25 percent of their daily caloric intake with one day of eating 175 percent of their daily caloric intake. For the average man's diet, a male participant would have eaten 650 calories on the fasting days and 4,550 calories on the feasting days. To test antioxidant supplements, the participants repeated the diet but also included vitamin C and vitamin E.

At the end of the three weeks, the researchers tested the same health parameters. They found that the beneficial sirtuin proteins such as SIRT 3 and another, SIRT1, tended to increase as a result of the diet. However, when antioxidants were supplemented on top of the diet, some of these increases disappeared. This is in line with some research that indicates flooding the system with supplemental antioxidants may counteract the effects of fasting or exercise, said Christiaan Leeuwenburgh, Ph.D., co-author of the paper and chief of the division of biology of aging in the department of aging and geriatric research.

The researchers found that the intermittent fasting decreased insulin levels in the participants, which means the diet could have an anti-diabetic effect as well.

"The hypothesis is that if the body is intermittently exposed to low levels of oxidative stress, it can build a better response to it," said Martin Wegman, an M.D.-Ph.D. student at the University of Florida College of Medicine and co-author of the paper recently published in the journal Rejuvenation Research.  

"You need some pain, some inflammation, some oxidative stress for some regeneration or repair," Leeuwenburgh said. "These young investigators were intrigued by the question of whether some antioxidants could blunt the healthy effects of normal fasting."

On the study participants' fasting days, they ate foods such as roast beef and gravy, mashed potatoes, Oreo cookies and orange sherbet -- but they ate only one meal. On the feasting days, the participants ate bagels with cream cheese, oatmeal sweetened with honey and raisins, turkey sandwiches, apple sauce, spaghetti with chicken, yogurt and soda -- and lemon pound cake, Snickers bars and vanilla ice cream.

"Most of the participants found that fasting was easier than the feasting day, which was a little bit surprising to me," Guo said. "On the feasting days, we had some trouble giving them enough calories."

Leeuwenburgh said future studies should examine a larger cohort of participants and should include studying a larger number of genes in the participants as well as examining muscle and fat tissue.