He added, however, that some people might consider calorie reduction possible by combining it with other popular nutritional strategies such as the Mediterranean diet, intermittent fasting, or reduced carbohydrate intake.
The new study provided clues as to how difficult calorie restriction can be. Study participants underwent an intensive training program, learning how to cook low-calorie meals, attending group sessions, and regularly checking in with nutrition experts. Yet they could not even reach half of the 25 percent calorie reduction target. And as anyone who diets knows, the hardest part of losing weight over the long term can be the most difficult part.
Although the calorie goal they set was high, they gave the subjects some flexibility and enabled them to eat the foods they wanted. What they found was that the subjects did not change their protein intake, but ate significantly less fat and slightly fewer carbohydrates. They also consumed more micronutrients such as vitamins A, K and magnesium, indicating a large increase in fruits and vegetables, said Susan B. Roberts, co-author of the study and Senior Scientist at the U.S.D.A. Human Nutrition Research Center on Aging at Tufts University.
"They ate healthier foods," she said. "Things like nuts, whole grains, green vegetables and legumes."
For many people, dieting can be an unpleasant experience. The researchers found, however, that calorie reduction was surprisingly unbearable in many subjects. While more people left the diet group than the control group, overall the study had a high retention rate. The researchers studied measures to measure quality of life and found that the calorie-reduced group reported better sleep, more energy and better mood. They also had no significant increase in hunger or food cravings compared to the control group. Roberts. One question that the study was unable to answer was whether calorie restriction could extend the lifespan of humans like other animals. The researchers would need to keep people up to date and follow them for many decades to test it out.