Will eating less lead to a longer life span?
with Dr Walter Chin
December 15, 2002
Although this is probably not the most appropriate time to discuss this topic, as Guyanese prepare to feast during the Christmas season, it has been recently reported that studies in rodents, yeast and other organisms have found that cutting down on calories extends the life span.
These studies have demonstrated that reducing an animal's intake of calories by 30 per cent will lengthen its life span by 30 per cent longer than those on an ordinary diet. The concept that a calorie-restricted diet could prolong life had been put forward by Dr Roy Walford, a professor at the University of California, Los Angeles, for the past three decades.
Dr Walford's idea originated in the early 1970s when he began studying the biology of aging. His initial studies showed that mice who were deprived of regular food outlived their normally fed counterparts by as much as two years - nearly doubling their normal life span. In addition, the risk of cancer and cardiovascular disease was lowered, and there seemed little adverse impact upon mental and physical function.
Some of the benefits were confirmed through participation in Biosphere 2, an experiment inside a self-contained ecosystem meant to test whether humans could live on the moon or Mars. Shortly into the experiment, the researchers found out that they would not be able to produce as much food as originally thought, so forcing the participants to go on a low calorie diet. Although the study was not long enough to be conclusive for humans, many benefits were derived from this diet. Men lost nearly 20 per cent of their body weight, while women dropped around 10 per cent. Blood pressure, blood sugar, cholesterol and triglycerides all fell by 20 per cent or more to extremely healthy levels. And the researchers demonstrated an enhanced capacity to fight off common illnesses like colds and influenza.
It is not known why reducing calorie intake leads to increased longevity. When the body takes in a surplus of calories, the body must cope with processing more nutrients than are needed. On the other hand, if the calorie intake is reduced, the body need not work so hard and it remains in better balance. When an organism appreciates that less food is available, it slows down its metabolism to conserve energy. As its metabolism goes into a lower gear, it reduces the production of toxic waste materials. It seems that this slower rate of activity translates into a longer life span.
In worms, calorie restriction results in impressive benefits. The worms become immune to heat and chemicals that would otherwise kill worms on a more normal diet. Monkeys on calorie restriction but with a diet fortified with extra vitamins and nutrients live a longer and healthier life than other monkeys on a fuller diet.
As there is no magic pill that has been proved to extend the human life span, scientists are now trying to find out if the same severely restricted diet that has produced dramatic results in laboratory animals will work in humans. In September, the National Institute on Aging began clinical trials involving 200 people. The trials will look at methods of reducing the calorie consumption. One approach will be to restrict the calorie intake; another will be a combination of partially reduced calorie intake and exercise. The study will see if a significant reduction in calories will improve health and enhance the likelihood of a longer life span. Finding a regimen that delivers maximum nutrition while sharply reducing calories is a key goal of the project.
Because the human life span is much longer than that of laboratory animals, researchers will not know for a generation or more whether the calorie-restricted diet actually helps humans live significantly longer. It is not expected that such a diet will completely stop heart attacks and strokes, but it is hoped that heart attacks will occur at an older age, rather than in middle-aged persons, as now commonly occurs.
Some of the volunteers in the study will have to lessen their usual consumption of calories by 25 per cent. This means that if someone has been consuming a diet of around 2000 calories, that person will be asked to cut back to 1500 calories.
It is not expected that this will be an easy task. It is relatively easy to control the habits of animals with food given out carefully each day by a researcher. It will be much harder to control the calorie intake of human beings.
Researchers assert that if calorie restriction works in human beings as it has in animals, people who now live into their 80s would routinely live until the age of 110 or beyond - and the extra years would be healthy ones. They would eventually succumb to cancers, strokes and heart attacks just as people do now, but at a more advanced age.
While this study has just begun, other scientists recently reported that they have made progress in understanding how eating less leads to longer life.
In a report in the journal Science, researchers announced that studies with fruit flies, which have many genes similar to mammals, showed that an enzyme called Rpd3 histone deacetylase is likely to be a key to longevity. When the level of the enzyme is decreased without eating less, there is still life extension. In the study, flies with genetic mutations that resulted in lower levels of the enzyme lived from 33 per cent to 50 per cent longer than normal. With a low calorie diet, the life span was extended by 41 per cent.
The enzyme could be lowered by a drug - phenylbutyrate. A study has already shown that feeding the drug to fruit flies extended their lives.
A menu that would restrict the number of calories would consist of the following. For breakfast: cereal with bran, fruit (banana), and a glass of skimmed milk. For lunch: a small portion of fish, cabbage, a slice of whole-wheat bread, and a glass of skimmed milk. For dinner: seafood, pasta, steamed callaloo, and a slice of water-melon. The total number of calories would be around 1300-1400. The percentage of calories from protein would be around 26 per cent; from fat 14 per cent; and from carbohydrates 60 per cent.
Those who are on a calorie-restricted diet concede that hunger can be a problem initially, but not a serious or lasting one. Most of those who go on sustained calorie restriction feel hungry during the first few months, but as the body adjusts to the new arrangements, the hunger pangs eventually wane. Since calorie-restrictive dieters eat so little, they must be certain that their food contains the proper nutrients.
As for special occasions and holidays, those on calorie restriction say they have no difficulty. Since they are already accustomed to eating much less than the average person, they do not find it impossible to resist the temptations of a big meal. In addition, their bodies probably will not be able to tolerate foods high in sugar or fat any more. Also, a person does not have to be on the diet every meal. If too much is eaten on one day, it simply means that less should be eaten on the following day.
So while following a calorie-restricted regimen this Christmas season will be a daunting challenge, it is not insurmountable.
A very Merry Christmas to all.