You’ve probably heard of calorie restriction or intermittent fasting, and you might wonder why these practices are gaining such widespread popularity.
In this article, we aim to clarify these definitions, in the hope that people can avoid misunderstanding these concepts and, consequently, applying these models inappropriately, fueling erroneous expectations.
1. Calorie restriction
Let's start with calorie restriction . The term can be misleading, since it does not refer to a diet that limits daily caloric intake below needs .
Caloric restriction involves reducing the average caloric intake below what is usually consumed, but without causing nutritional deficiencies or deprivation of essential nutrients. In the numerous studies conducted on this topic, most of the participants were habitually following a hypercaloric diet, that is, about 4000 kcal per day.
They were then put on a diet plan that aimed to reach an energy intake considered normocaloric, that is, an amount similar to what their metabolism would have been able to burn during the day."
2. Intermittent fasting
In the context of a fasting diet , an individual may choose to abstain from food completely or significantly limit their food intake only at certain times of the day, week, or month.
These dietary patterns are being studied extensively as potential tools for maintaining good health and prolonging longevity. It should be emphasized that these are not just temporary weight loss plans.
IMPORTANT
Interest in them, for their potential health and anti-aging benefits, has grown through decades of research in a variety of animal species, including worms, crabs, snails, fruit flies, and rodents.
In several experiments, the adoption of calorie-restricted diets has been shown to delay the onset of age-related disorders and, in some cases, to extend lifespan.
3. But what evidence is there on caloric restriction in humans?
Given these animal findings, researchers are now studying whether and how calorie restriction or fasting affects health and lifespan in people.
Some studies suggest that calorie restriction may have benefits for human health, but more research is needed to understand its long-term effects.
We would like to point out that there is no human data on the relationship between caloric restriction and longevity.
4. Avoid low-calorie diets
Some people have voluntarily practiced extreme forms of calorie restriction for many years, believing that it can prolong life or preserve health.
Studies conducted on these individuals have found very low levels of risk factors for cardiovascular disease and diabetes.
However, these studies have also highlighted some physiological changes that underline some possible long-term risks, for example the reduction of sexual interest and the ability to maintain body temperature in cold environments , decreased muscle mass, decreased bone mass.
Another confounding factor in people who benefited from calorie restriction was that many were usually taking dietary supplements, making it difficult to distinguish the effects of calorie restriction from those of other factors.
5. More rigorous studies on humans
To conduct a more rigorous study of calorie restriction in humans, the National Institute on Aging (NIA) supported a pioneering clinical trial called the Comprehensive Assessment of Long-term Effects of Reducing Intake of Energy (CALERIE).
In CALERIE, 218 young and middle-aged adults with normal weight or moderately overweight were randomly divided into two groups.
People in the experimental group were asked to follow a calorie-restricted diet for 2 years, while those in the control group continued their usual diet.
The experimental group following a calorie restriction diet reduced their daily calorie intake by 12% and maintained, on average, a 10% body weight loss over the course of 2 years .
A follow-up study conducted 2 years after the intervention ended found that participants had maintained much of this weight loss.
Additionally, a reduction in risk factors (lower blood pressure and lower cholesterol) for age-related diseases such as diabetes , heart disease and stroke was observed.
They also showed a decrease in some inflammatory factors and thyroid hormones.
It is therefore important to underline that calorie restriction regimes should not be interpreted as starvation diets or low-calorie diets , which increase the risks associated with loss of bone mass, loss of muscle, reduced libido and malnutrition due to subclinical micronutrient deficiencies.
More and more studies show that by reducing the time window for eating to 8-10 hours, for example 7 until 5 pm and bringing forward the last meal of the day, it is possible to reduce fat mass more easily with the same amount of calories ingested.
6. Conclusion: What is the safest and most sustainable long-term calorie restriction diet?
The ideal so-called “caloric restriction” diet is therefore a normocaloric one, meaning reducing the amount of calories that were ingested in excess.
So a nutritional plan that can provide the same amount of calories that your metabolism is able to burn during the day, while integrating key micronutrients such as minerals, vitamins, essential amino acids and polyphenols.
This approach aims to overcome the challenge of increasingly nutrient-deficient modern foods, which can slow down metabolism.
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GO TO THE NUTRITIONAL TESTSources:
- Calorie restriction and fasting diets: What do we know? National Institute on Aging 2018
- Intermittent Fasting versus Continuous Calorie Restriction: Which Is Better for Weight Loss? Nutrients 2022, 14(9), 1781;
- Calorie and Time Restriction in Weight Loss; N Engl J Med 2022 Apr 21;386(16):1572-1573; doi: 10.1056/NEJMe2202821
