TL;DR

Intermittent fasting limits when you eat instead of focusing only on what you eat. Research suggests it can help with weight loss, improve insulin sensitivity, lower blood sugar, and support metabolic health. Common approaches include a 12-hour overnight fast, a 16:8 schedule, and one meal a day (OMAD). However, intermittent fasting is not right for everyone, especially people with significant stress or adrenal problems.

What Is Intermittent Fasting?

Intermittent fasting means eating during a set window each day and fasting the rest of the time. During the fasting period, insulin levels fall and your body begins using stored fat for energy. Unlike many diets, intermittent fasting does not require counting calories or eliminating specific foods.

Common Intermittent Fasting Schedules

12:12 (Good for Beginners)

Eat during a 12-hour window and fast for 12 hours overnight.

Example:

  • Breakfast: 7:00 AM
  • Dinner finished by 7:00 PM

Many people naturally follow this schedule, and it may be enough to improve blood sugar and reduce late-night snacking.

16:8 (Most Popular)

Eat during an 8-hour window and fast for 16 hours.

Example:

  • First meal: 10:00 AM
  • Last meal: 6:00 PM

This is the schedule most often studied. Research suggests it may improve insulin sensitivity, help with weight loss, and lower the risk of type 2 diabetes.

One Meal a Day (OMAD)

Some people eat all of their daily food in one meal.

While some people do well with this approach, others find it difficult to eat enough protein, vitamins, and minerals in a single meal. It is generally more challenging than a 16:8 schedule and is not necessary for most people.

Is Intermittent Fasting Right for Everyone?

No.

Some people feel worse when fasting, especially those with chronic stress, adrenal dysfunction, poor sleep, or very high cortisol levels. Fasting may increase stress hormones in susceptible individuals, leading to fatigue, dizziness, irritability, or difficulty sleeping.

If fasting makes you feel worse instead of better, choose a less restrictive schedule or stop altogether. Healthy eating is more important than following a fasting clock.

People taking insulin or medications that lower blood sugar should discuss intermittent fasting with their healthcare provider before making major changes.

Bottom Line

Intermittent fasting is a simple tool that may improve weight loss, insulin resistance, and blood sugar control. A 12-hour overnight fast is a good place to start, while a 16:8 schedule has the strongest research behind it. More aggressive approaches, such as one meal a day, may work for some people but are not necessary for most.

Check the Research:

  1. Intermittent versus daily calorie restriction: which diet regimen is more effective for weight loss? Obes Rev. 2011;12:e593–601
  2. .Anton S, Leeuwenburgh C. Fasting or caloric restriction for healthy aging. Exp Gerontol. 2013;48:1003–5. doi: 10.1016/j.exger.2013.04.011.
  3. Harvie M, Wright C, Pegington M, McMullan D, Mitchell E, Martin B, et al. The effect of intermittent energy and carbohydrate restriction v. daily energy restriction on weight loss and metabolic disease risk markers in overweight women. Br J Nutr. 2013;110:1534–47. 
  4. Barnosky AR, Hoddy KK, Unterman TG, Varady KA. Intermittent fasting vs daily calorie restriction for type 2 diabetes prevention: a review of human findings. Transl Res. 2014;164:302–11. 
  5. Mattson MP, Longo VD, Harvie M. Impact of intermittent fasting on health and disease processes. Ageing Res Rev. 2017;39:46–58.
  6. Jebeile H, Gow ML, Lister NB, Mosalman Haghighi M, Ayer J, Cowell CT, et al. Intermittent energy restriction is a feasible, effective, and acceptable intervention to treat adolescents with obesity. J Nutr. 2019;149:1189–97.
  7. Stekovic S, Hofer SJ, Tripolt N, Aon MA, Royer P, Pein L, et al. Alternate day fasting improves physiological and molecular markers of aging in healthy, non-obese humans. Cell Metab. 2019;30:462–76. 
  8. Hu D, Xie Z, Ye Y, Bahijri S, Chen M. The beneficial effects of intermittent fasting: an update on mechanism, and the role of circadian rhythm and gut microbiota. Hepatobiliary Surg Nutr. 2020;9:597–602.