Fads come and go in the health and wellness space.

When it comes to fasting, expect this one to stick around for the long-term.

Unlike harmful diuretic weight loss pills, cabbage juice dieting, or the Thigh Master, fasting comes in many forms to fit the unique needs of the patient. These include fasting mimicking diets, intermittent fasting, weekly 24-hour fasts, alternate day fasting and more aggressive, extended fasts that require medical supervision.1

Fasting was initially studied for its benefit in weight loss, but as more data is published, there are now significant reasons to consider fasting apart from a number on the scale.1,2,7

These benefits include a reduction in reactive oxygen species and inflammation, blood pressure, and cholesterol levels, not to mention improvements in the gut microbiome, immune system efficiency and autophagy.1-7

Types of Fasting

Fasting comes in many forms and choosing the right protocol will be an important conversation to have with your patients. The selection must be taken on an individual basis, considering the patient’s health history, preferences, religious practices, additional dietary goals such as ketosis, as well as if broths will be consumed during the fasting period.1




Additional Considerations

Time-restricted eating

Every day

16 hours

Eating occurs during eight hours of the day, usually early in the day after rising from bed. A more restrictive variant limits eating to six hours during the day and fasting occurs for 18 hours.

Alternate day fasting

Every other day

24 hours

One approximately 500 calorie meal is consumed at about the mid-point (about 12 hours) of a 24-hour period. For example, in one study, subjects were “instructed to consume 25% of baseline energy intake as a lunch (between 12pm and 2pm) on fasting days…” When a meal is included, technically this is a non-fasting, very-low-calorie regimen or “partial fast.”

5:2 diet

Twice per week

24 hours

One 500–600 calorie meal is consumed on the fasting day. For example, one study instructed subjects to follow “a diet of 500 to 600 kcal/day for 2 days of the week…”  and most fasting days were non-consecutive. When a meal is included, technically this is a non-fasting, very-low-calorie regimen, or “partial fast.”

Weekly one-day fasting

Once per week

24 hours

A water-only fasting regimen

Fasting mimicking diet

Once per month

120 hours

A low-calorie, non-fasting ketogenic diet; this is a non-fasting regimen that allows for small maximum amounts of macronutrients

10-day juice fast

Irregular frequency

240 hours

Fruit juices or broths are consumed during the fasting period, but no solid foods

Other regimens



Many possible frequency- and timing-based approaches are possible

Cardiometabolic Benefits of Fasting

Intermittent fasting has shown to have a consistent impact on weight loss, with research showing the varied forms of fasting produce a 1-8% loss from baseline measurements. In addition, a consistent drop in energy intake was shown, with data ranging from 10%-30% drop from baseline.2

In a randomized controlled trial comparing intermittent fasting with calorie restriction in healthy overweight premenopausal women, the authors found similar improvements in weight loss, body fat and waist measurement, but only the intermittent fasting group saw a greater improvement in insulin sensitivity, measured by HOMA-IR, as well as increases in adiponectin compared to caloric restriction.3

Another prospective observational trial investigating the effect of fasting on fatty liver index in patients with and without type 2 diabetes (T2D) found improvements in both populations. Subjects with T2D showed a greater reduction in fatty liver than subjects without T2D.4

Possible Risks of Fasting

Let’s be clear, for all the benefits of fasting, there are certain populations with unique risks that should not engage in fasting. This includes patients with a history of eating disorders, pregnant and lactating women, young children, the elderly, and patients who have undergone organ replacement and are on immunosuppression medication.

It’s Important to make the distinction, however, that while fasting is not recommended for patients with a history of disordered eating, research does not show a predictable disturbance in energy levels or an increase in disordered eating in populations that don’t have a known history or risk.2

The Bottom Line

Fasting has shown many benefits for patients with and without cardiometabolic risk, and practitioners need to guide patients toward the appropriate form that is right for them. This also includes ongoing monitoring to make sure patients are following the diet appropriately and to lower the risk of macronutrient and micronutrient deficiencies.

Dietary interventions are just the tip of the iceberg, and there is much more a keen clinician needs to understand to properly manage cardiometabolic risk. They must also be able to address their patients’ stress levels, gut health, including healing intestinal permeability and dysbiosis, as well as supporting immune function and hormonal balance.




Steven Imgrund, MS, CNS Headshot

Steven Imgrund is a board-certified nutritionist. Steven developed his passion for nutrition and health working as personal trainer and health coach, specializing in weight loss and behavior change. Through working with hundreds of clients, Steven has seen the challenges with implementing long-term lifestyle and dietary habits. This experience has fueled his passion for functional medicine, and his desire to help health care practitioners use proven lifestyle and supplement strategies to safely address the root causes of their patients cardiometabolic issues. Steven received his Masters in Human Nutrition through Bridgeport University in 2018, and Certified Nutrition Specialist (CNS) certification in 2020.


  1. Grajower MM, Horne BD. Clinical Management of Intermittent Fasting in Patients with Diabetes Mellitus. Nutrients. 2019;11(4):873. doi:10.3390/nu11040873
  2. Varady KA, Cienfuegos S, Ezpeleta M, Gabel K. Cardiometabolic Benefits of Intermittent Fasting. Annual Review of Nutrition. 2021;41(1):333-361. doi:10.1146/annurev-nutr-052020-041327
  3. Harvie MN, Pegington M, Mattson MP, et al. The effects of intermittent or continuous energy restriction on weight loss and metabolic disease risk markers: a randomized trial in young overweight women. International Journal of Obesity. 2010;35(5):714-727. doi:10.1038/ijo.2010.171
  4. Drinda S, Grundler F, Neumann T, et al. Effects of Periodic Fasting on Fatty Liver Index—A Prospective Observational Study. Nutrients. 2019;11(11):2601. doi:10.3390/nu11112601 de Cabo R, Mattson MP. Effects of Intermittent Fasting on Health, Aging, and Disease. Longo DL, ed. New England Journal of Medicine. 2019;381(26):2541-2551.
  5. Bagherniya M, Butler AE, Barreto GE, Sahebkar A. The effect of fasting or calorie restriction on autophagy induction: A review of the literature. Ageing Research Reviews. 2018;47:183-197. doi:10.1016/j.arr.2018.08.004
  6. Jamshed H, Beyl RA, Della Manna DL, Yang ES, Ravussin E, Peterson CM. Early Time-Restricted Feeding Improves 24-Hour Glucose Levels and Affects Markers of the Circadian Clock, Aging, and Autophagy in Humans. Nutrients. 2019;11(6):1234. doi:10.3390/nu11061234