Calorie restriction, low-calorie diet and intermittent fasting: let's understand the differences

You've probably heard of calorie restriction or intermittent fasting before, 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 inadequately, fueling incorrect expectations.

1. Calorie restriction

Let's start with the calorie restriction. The term could be misleading, since does not refer to a diet that limits daily calorie intake below needs.

Caloric restriction involves reducing the average caloric intake below what is usually consumed, without however leading to nutritional deficiencies or deprivations of essential nutrients. In the numerous studies conducted on this topic, the majority of participants habitually followed a high-calorie diet, which means around 4000 kcal per day.

They were subsequently subjected to a food plan that aimed to achieve an energy intake considered normocaloric, i.e. a quantity 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 to only certain times of the day, week, or month.

These dietary patterns are the subject of in-depth studies as possible tools for maintaining good health and prolonging longevity. It should be emphasized that these are not simply temporary weight loss plans.


The interest in them, regarding the potential advantages on health and aging, has developed through decades of research conducted on a variety of animal species, including worms, crabs, snails, fruit flies and rodents.

In many experiments, the adoption of calorie-restricted diets has demonstrated the ability to delay the onset of age-related disorders and, in some cases, extend lifespan.

3. But what evidence is there for calorie restriction in humans?

Given these animal findings, researchers are studying whether and how calorie restriction or a fasting diet 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 specify that there is no human data regarding 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 it will prolong life or preserve health.

Studies of these individuals have found very low levels of risk factors for cardiovascular disease and diabetes.

However, these studies have also highlighted some underlining physiological changes some possible long-term risks, for example reduced sexual interest and ability to maintain body temperature in cold environments, decreased muscle mass, decreased bone mass.

Another confounding factor for people who benefited from calorie restriction is that many typically took dietary supplements, making it difficult to distinguish the effects of calorie restriction from those of other factors.

5. More rigorous human studies

To conduct a more rigorous study of calorie restriction in humans, the National Institute on Aging (NIA) supported a pioneering clinical study called 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-restricted diet reduced 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.

Furthermore, a reduction in risk factors (lower blood pressure and lower cholesterol) for age-related diseases such as diabetes was noted , diseases heart e ictus.

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 related to bone loss, muscle loss, reduced libido and malnutrition from subclinical micronutrient deficiencies.

More and more studies show that by reducing the time window for eating to 8-10 hours, for example 7 to 17.00 pm and bringing forward the last meal of the day, it is possible to reduce fat mass more easily with the same 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 ingested in excess.

Then a a nutritional plan capable of providing the same amount of calories that your metabolism is able to burn during the day, while integrating the main 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 metabolism.

Do you want to know which diet is right for you?

Access our online nutrition test now to receive specific nutritional advice and a personalized food plan which will help you live a healthy life.

Take control of your life and take a proactive approach to your well-being.


  1. Calorie restriction and fasting diets: What do we know? National Institute on Aging 2018
  2. Intermittent Fasting versus Continuous Calorie Restriction: Which Is Better for Weight Loss? Nutrients 2022, 14(9), 1781;
  3. Calorie and Time Restriction in Weight Loss; N Engl J Med 2022 Apr 21;386(16):1572-1573; doi: 10.1056/NEJMe2202821
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