This article was first published on September 23, 2022. It was last edited or updated on September 23, 2022.
As of September 2022, intermittent fasting has become quite a fad. I hear about it everywhere—in the media, from my patients, and from family members and friends. But I think the people who practice and recommend intermittent fasting typically don’t know much about what research on this topic has found.
Also, mental health patients, especially those who are on medications, so frequently struggle with weight gain and other metabolic problems that I think mental health clinicians need to learn all they can about ways to help with these problems.
So, let’s look into intermittent fasting to see if it could be one of the strategies that we recommend to our patients.
The first thing to realize is that there are 3 different types of intermittent fasting:
It is also called “time-restricted feeding”. This is the one that seems to be the most popular. As the name suggests, the person is supposed to eat only within a defined period of the day (“window”) and to fast the rest of the time. The rest of the time, the person can only take water or zero-calorie beverages like black coffee.
The duration of the fasting period varies—it is most frequently 16 hours but some people fast for 14 or 20 hours a day. These are referred to as 16:8, 14:10, or 20:4.
For example, the person may eat only between 8 am and 4 pm and fast from 4 pm to 8 am (16 hours of fasting; for example, Liu et al., 2022). Or, eat from 12 pm to 8 pm and fast from 8 pm to 12 noon (16 hours of fasting).
Time-restricted eating is attractive to many people because of its simplicity and because during the period that those practicing this method can eat, supposedly they can eat anything they want. But, many people combine time-restricted eating with calorie restriction.
As the name suggests, alternate-day fasting involves fasting on alternate days. The fast days are alternated with “feast” days.
There are two different ways in which the fast days can be conducted. On fast days, the person could consume (Varady et al., 2020:
1. Only water or zero-calorie beverages
2. 25% of their energy needs or about 500 kcal per day. This has been called “modified alternate day fasting”.
On “feast” days, persons practicing alternate-day fasting can eat anything they want and as much as they want!
The 5:2 diet
The 5:2 diet consists of five “feast days” and two “fast days” each week. That’s why it is called the 5:2 diet.
– On feast days, they can eat anything they want.
– On the two fast days of the week, they eat a restricted number of calories, typically 500 to 1,000 kcal per day (Varady et al., 2022).
The two fast days can be either consecutive or non-consecutive days of that week (Varady et al., 2022).
Next, please see the following other articles about intermittent fasting on this website:
Fanti M, Mishra A, Longo VD, Brandhorst S. Time-Restricted Eating, Intermittent Fasting, and Fasting-Mimicking Diets in Weight Loss. Curr Obes Rep. 2021 Jun;10(2):70-80. doi: 10.1007/s13679-021-00424-2. Epub 2021 Jan 29. PMID: 33512641.
Joaquim L, Faria A, Loureiro H, Matafome P. Benefits, mechanisms, and risks of intermittent fasting in metabolic syndrome and type 2 diabetes. J Physiol Biochem. 2022 May;78(2):295-305. doi: 10.1007/s13105-021-00839-4. Epub 2022 Jan 5. PMID: 34985730.
Patikorn C, Roubal K, Veettil SK, Chandran V, Pham T, Lee YY, Giovannucci EL, Varady KA, Chaiyakunapruk N. Intermittent Fasting and Obesity-Related Health Outcomes: An Umbrella Review of Meta-analyses of Randomized Clinical Trials. JAMA Netw Open. 2021 Dec 1;4(12):e2139558. doi: 10.1001/jamanetworkopen.2021.39558. PMID: 34919135; PMCID: PMC8683964.
Santos HO, Genario R, Tinsley GM, Ribeiro P, Carteri RB, Coelho-Ravagnani CF, Mota JF. A scoping review of intermittent fasting, chronobiology, and metabolism. Am J Clin Nutr. 2022 Apr 1;115(4):991-1004. doi: 10.1093/ajcn/nqab433. PMID: 34978321.
Yuan X, Wang J, Yang S, Gao M, Cao L, Li X, Hong D, Tian S, Sun C. Effect of Intermittent Fasting Diet on Glucose and Lipid Metabolism and Insulin Resistance in Patients with Impaired Glucose and Lipid Metabolism: A Systematic Review and Meta-Analysis. Int J Endocrinol. 2022 Mar 24;2022:6999907. doi: 10.1155/2022/6999907. PMID: 35371260; PMCID: PMC8970877.
Varady KA, Cienfuegos S, Ezpeleta M, Gabel K. Clinical application of intermittent fasting for weight loss: progress and future directions. Nat Rev Endocrinol. 2022 May;18(5):309-321. doi: 10.1038/s41574-022-00638-x. Epub 2022 Feb 22. PMID: 35194176.
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