Are crash diets really more effective for weight loss? | Press room



Studies are looking at whether intermittent diets improve people’s nutritional balance. Credits to Julia Zolotova on Unsplash

In magazines and social networks, crash diets are on the rise. From influencers touting their experience to pseudo-experts feeding their blogs advice to get everyone started, the internet has been carrying this trend for several years. However, the term “crack diet” covers many realities, with diverse practices (see box). Their common point is always to alternate more or less prolonged periods of dietary restrictions with periods when you can eat normally.

This type of diet is often presented as being more effective in promoting weight loss. Some in particular believe that it makes it possible to avoid the potential restrictions and frustrations associated with constant food restrictions, and thus leads to better adherence. Others highlight beneficial effects on metabolic parameters (blood pressure, blood sugar, cholesterol, etc.), or even for the prevention of specific diseases (cancer, inflammation, metabolism, cardiovascular disease, etc.).

It should be noted, however, that well-constructed scientific studies, with solid methodologies, still lack a proper evaluation of these diets and their effects on different population groups. Furthermore, even when interesting results are obtained, it can be difficult to generalize to all crash diets due to the heterogeneity of practices.

So what can be said about the effect of crash dieting on weight loss? Is it more effective than other diets in the long term? What is its effect on eating behaviour? Canal Detox explores these questions.

The most popular of the intermittent diets

  • The 5:2 diet It consists of eating normally for 5 days and then significantly reducing the number of calories over the next 2 days (500 calories/day for women and 600 calories/day for men).
  • Diet 16/8 It consists of fasting during the day for the 14 to 16 hours and eating meals for the remaining 8 to 10 hours (eg you can have a snack at 4 pm and not eat anything until the next morning).
  • L’Alternating day fasting He fasts every day.

Intermittent diets are no more effective than other diets

The main promise of intermittent diets is to facilitate weight loss while relieving stress compared to other restrictive diets. But when we look at the most rigorous studies or reviews of the scientific literature (meta-analyses), we realize that the results are variable. Most publications do not show any superiority of the crash diet (regardless of its modalities) over other diets in terms of weight loss.

Among the studies published on this topic with rigorous methodology, let’s quote a few that were particularly interested in the 5:2 diet (5 days free and 2 days with very low calorie consumption).

published work inInternational Journal of Obesity It was conducted on 332 obese subjects, divided into three groups (continuous restriction while reducing the number of calories consumed each day; alternating restriction every two weeks and the classic 5:2 intermittent restriction). After 12 months, 146 subjects had completed the study, with similar moderate weight loss in the three groups (6.6 kg, 5.1 kg, and 5 kg, respectively, on average).

Similar results were seen in a study of 109 people followed for 24 months, with similar weight loss in the first year on the three types of diets and stabilization between 12 and 24 months. However, it is not possible from this data to draw conclusions regarding other types of intermittent diets.

These different studies also looked at critical metabolic parameters of health, especially cardiovascular, without being successful in showing the superiority of one diet over the other. In studies comparing the 5:2 diet to traditional, restrictive diets, for example, if total cholesterol, blood sugar levels, and triglycerides were reduced[1] It remained the same in all groups. Similarly, in the study comparing these diets to an unrestricted diet, no differences were found in metabolic parameters.

If, therefore, intermittent diets are no less effective than others for weight loss, they cannot be considered a “miracle diet”. Especially since other factors must be taken into account, for example their effect on appetite and food balance.

Here again, the data from the research is quite heterogeneous. However, we can cite findings that continuous restricted dieting can be associated with greater improvement in food balance, with consumption of more varied meals and healthier habits than intermittent diets.

It remains unclear whether people on crash diets “overcompensate” by eating more food during the times when they are allowed to do so.

Finally, it should be emphasized that long-term adherence to diets, whether sporadic or not, is often low. In many studies, we’ve observed participants abandon the diet along the way, with the risk of regaining lost weight. Promoting a balanced diet with medical support, and also emphasizing regular meal times and physical activity, remains an effective approach for many individuals.

Moving forward: A selection of studies on weight, appetite, and metabolic parameters

Sundfør TM, Tonstad S., Svendsen M. Effects of intermittent versus continuous energy restriction of weight loss on diet quality and eating behaviour. randomized trial. Eur J Clin Nutr. 2019; 73 (7): 1006-1014

Gosby MR, Roy M, Brown RC, et al. Paleolithic intermittent fasting, or the Mediterranean diet in the real world: Exploratory secondary analyzes of weight loss experience that included diet choice and exercise. Am J Clin Nutr. 2020; 111 (3): 503–514

Roman YM, Dominguez MC, IsoTM, et al. Effects of intermittent dieting versus continuous dieting on weight and body composition in obese and overweight subjects: a systematic review and meta-analysis of randomized controlled trials. Int J Opis (London). 2019; 43(10): 2017–2027

Coutinho SR, Halsett EH, Gasbak S, et al. Activation of compensatory mechanisms with intermittent energy restriction: a randomized control trial. Cholesterol wink. 2018; 37 (3): 815-823. doi: 10.1016/j.clnu.2017.04.002

Trebanowski JF, Kruger CM, Barnowski A, et al. Effect of alternate day fasting on weight loss, weight maintenance and heart protection among healthy obese adults: a randomized clinical trial. Gamma Intern Med. 2017

Cracked diet, effect on other diseases: an example of cancer

An entire section of scientific research has also begun to focus on the link between crash diets and the development of diseases, particularly cancer. However, the results must be taken with caution because they were obtained in animal models. For example, an intermittent diet had beneficial effects in an obese mouse model with breast cancer, slowing tumor growth and reducing lung metastasis without the animals losing weight otherwise. However, these conclusions cannot be generalized to humans at present in the absence of rigorous clinical trials.

Finally, it should be noted that for cancer patients, as mentioned in an article I quotedAmerican Cancer SocietyIf preclinical studies suggest that intermittent diets can reduce the toxicity of chemotherapy, then their risks—particularly with regard to malnutrition—are much greater.

In conclusion, while crash diets appear to be generally safe for healthy individuals and may help reduce weight in some overweight people, their superiority over other diets is uncertain. In addition, questions remain about its impact on other parameters related to cardiovascular health. A well-balanced diet, based on the National Healthy Nutrition Program (PNNS), is recommended, along with regular physical activity, to promote weight loss and health.

[1] The percentage of lipids in the blood, the concentration of which is too high, increases the risk of cardiovascular disease


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