EATING less can dramatically reduce the risk of heart disease. 鈥淐aloric restriction鈥� in humans could also help prevent other diseases such as diabetes, stroke, and even cancer.
Until now, the benefits of caloric restriction (CR) have been observed only in animals, albeit among a wide variety ranging from worms to mice. The effects include increased lifespan and significantly reduced risk of cancer, coronary heart disease, diabetes, stroke and autoimmune diseases.
The only results for humans have been gleaned incidentally from other experiments. For instance, during the Biosphere 2 experiment, when eight people lived in a 1.28-hectare sealed environment in the Arizona desert, the participants ate less than normal as they grew their own food. After two years, they were found to have lower blood pressure and reduced cholesterol and triglyceride levels 鈥� all risk factors for heart disease.
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Now Luigi Fontana of the School of Medicine at Washington University in St Louis, Missouri, and his colleagues have conclusive proof that caloric restriction does have health benefits for people. In the first ever long-term study of the effects, the researchers followed 18 people who have been voluntarily practising CR for an average of six years, eating nutritionally balanced diets containing between 1112 and 1958 kilocalories a day. They were compared with 18 healthy control subjects, eating typical diets of 1976 to 3537 kilocalories a day. According to Fontana, the people on the CR diet are all healthy individuals who exercise in moderation and lead active lives.
Fontana鈥檚 team measured various factors that increase the risk of atherosclerosis, a disease characterised by hardening of the arteries, in each group. The team found the CR group had significantly lower levels of total blood cholesterol and triglycerides, as well as reduced blood pressure and extremely low levels of a blood protein called C-reactive protein, a marker for inflammation of arteries. The CR group also had no atherosclerotic plaque in their arteries 鈥� another strong predictor of heart attacks (Proceedings of the National Academy of Sciences, vol 101, p 6659).
Individuals in the CR group were much leaner, with an average body mass index of 19.5 compared to 26 in the controls, and an average total body fat of 6.7 per cent compared to 22.4 in the control group. 鈥淭hey have a reduced risk of coronary heart disease, stroke, heart failure, [adult onset] diabetes and most of the kidney diseases caused by high blood pressure,鈥� Fontana says. And he is optimistic that the other dramatic effect of this kind of diet in animals 鈥� sharply reduced rates of cancer 鈥� can also be expected in humans.
Richard Weindruch, an expert on CR at the University of Wisconsin in Madison, is impressed. 鈥淭his presents some of the clearest evidence that long-term caloric restriction in humans reduces the risk of developing disease.鈥� Intriguingly, Weindruch鈥檚 long-running studies are hinting that feeding rhesus monkeys less might increase their lifespan 鈥� an affect not yet seen in primates. 鈥淢ore animals are dying among the controls than in the CR group,鈥� he says. 鈥淏ut it鈥檚 a bit early to draw conclusions, except that the trends are pointing in that direction.鈥�
However, Fontana and Weindruch caution that people should only reduce their calorie intake under expert supervision. 鈥淚t can be harmful if you overdo caloric restriction, especially if you don鈥檛 have all the nutrients you need,鈥� Fontana says. Weindruch agrees. The regimen is difficult to follow, which limits its widespread use, he says.
More worryingly, Weindruch says the beneficial effects of CR highlight the consequences of the obesity epidemic in the US and Europe. If eating less lowers the risk factors associated with diseases, Weindruch says, it also shows how much higher the risks are when we eat too much.