It’s a tantalizing idea: Adapt your diet so that you consume fewer calories than your body burns and, as a result, you’ll live longer.
That’s the concept of “calorie restriction.” Some people have been following it for years, inspired by studies dating back to the 1930s that found calorie restriction can slow biological aging and extend lifespan in animal species including flies, rodents, dogs and rhesus monkeys.
But information from rigorous, well-controlled studies in humans has been lacking. Until now.
A study published online last month in the Lancet Diabetes and Endocrinology suggests that, when started in young adulthood and middle age, calorie restriction can have a significant impact on future health. What’s more, the benefits may be achieved with a relatively modest decrease in calorie intake.
What is calorie restriction?
Calorie restriction is not a short-term diet. Rather, it’s about consistently eating fewer calories – a 25-per-cent to 40-per-cent reduction has been used in animal experiments – while still consuming all the necessary protein, vitamins, minerals and other nutrients.
That’s a fundamental point. Calorie restriction necessitates eating nutrient-dense foods and monitoring intake of essential nutrients, because a calorie-reduced diet that’s deficient in amino acids, fatty acids and/or micronutrients isn’t going to bestow the health and longevity benefits.
The CALERIE study
The new Lancet study, called the Comprehensive Assessment of Long-Term Effects of Reducing Intake of Energy (CALERIE) trial, is the first to test the effect of calorie restriction on cardiometabolic risk factors in healthy young and middle-aged men and women. (Cardiometabolic risk factors contribute to a person’s chances of developing heart disease and metabolic disorders such as Type 2 diabetes.)
Blood pressure, blood cholesterol, blood triglycerides (fats), inflammatory markers, blood glucose and insulin sensitivity (that is, how well the body uses insulin to clear blood sugar) were among the cardiometabolic risk factors evaluated.
The randomized controlled trial assigned 213 adults, ages 21 to 50, to one of two groups: One group was instructed to reduce daily calorie intake by 25 per cent for two years, and the other group continued to follow their usual diets.
Participants’ individual calorie prescriptions were 25 per cent less than the total number of calories their bodies burned each day; total daily energy expenditure was measured by a scientific technique called the doubly labelled water method.
Participants were lean or just slightly overweight and already had cardiovascular and metabolic health markers in the normal range.
According to the researchers, factors such as blood pressure, LDL (bad) blood cholesterol and fasting blood sugar can increase the likelihood of developing heart disease and diabetes even when they are within ranges considered to be normal.
Over two years, the calorie-restriction group didn’t reach the 25-per-cent goal but did cut calories by 12 per cent, or 279 calories a day, the amount in 1.5 cups of white rice, a large bagel or 36 potato chips. The group also sustained an average weight loss of 16 pounds. (Calorie intake and body weight didn’t change in the control group.)
Calorie restriction also caused a significant reduction in all cardiometabolic risk factors, even though these values were normal to begin with. Participants who ate their usual diet did not experience any improvements.
The improvements in blood pressure, cholesterol, glucose, inflammatory markers and insulin sensitivity were over and above what would be expected from weight loss alone, hinting that calorie restriction itself plays a role.
The researchers concluded that a modest calorie restriction, when started in people who are young, healthy and not obese, may offer substantial protection from cardiovascular disease and diabetes later in life.
This study doesn’t prove that cutting 279 calories a day for two years will prevent heart disease or diabetes down the road. The researchers didn’t follow people long enough to find this out, nor did they measure changes in fatty plaques in participants’ arteries over the two years.
The participants were highly motivated and, as such, the findings might not be applicable to the general population.
Even so, this first-of-its-kind study has a number of strengths.
Daily calorie intake and energy expenditure were measured very carefully. The study had a large sample size considering the intensive dietary intervention, adherence to the calorie-restricted diet was high, and participant drop-out rate was low.
What to know before you try it
If you’re considering calorie restriction, I strongly recommend working with a dietitian to ensure that you are meeting all of your nutrient needs. Consult your doctor to get blood work done so you can track your improvements.
Make every calorie count. Simply cutting calories and not focusing on proper nutrition can lead to nutrient deficiencies that can affect bone health, immune function and concentration and memory.
Avoid sugary beverages, added sugars, junk food and alcoholic beverages, which contain empty calories. Replace refined (white) grains with whole-grain foods such as brown rice, quinoa, oats and whole-grain pastas.
Include nutrient-dense fruits, vegetables and protein foods such as fish, chicken, lean meat, eggs, beans, lentils and unsweetened yogurt.
Take nutrition supplements, such as multivitamin, if advised by your health-care provider.
Leslie Beck, a Toronto-based private practice dietitian, is director of food and nutrition at Medcan.
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