Intermittent, 24-hour, alternate day, or 5:2? The names may vary, but each of those is a form of fasting that has been touted as the ticket for everything from anti-aging to weight loss. But what is fasting exactly? Is there any science to support its use? 

Fasting has been around for years in various forms. It can be motivated by religion, health concerns, or even schedule issues. Fasting is simply not eating for a period of time. In its most basic form, the word “breakfast” means “breaking the fast”- eating after a period of being without food overnight.

Fasting is not a diet but instead is a pattern of eating and not eating.

Intermittent Fasting

One popular form of intermittent fasting (IF) is time-restricted feeding. This involves having a window of time when you can eat and a window of time when you can’t eat. An example is the 16:8 fast. In a 16:8 fast, an individual can eat within an 8-hour window (i.e., 11 AM to 7 PM) and then fast for 16 hours (7 PM to 11 AM). Water and other calorie-free liquids are allowed in the fasting time frame.

This type of fasting has the most research behind it. 

Intermittent Fasting and Weight Loss

Weight loss remains one of the top New Year’s resolutions. Can IF help?  A recent meta-analysis of studies evaluated the health outcomes of IF and discovered that various types of IF resulted in reduced body weight, BMI, fat mass, LDL cholesterol, total cholesterol, fasting blood sugar, and insulin.

Compared to a regular diet, alternate day fasting (every other day) for 1 to 2 months resulted in a drop in BMI in healthy adults and those who were overweight or obese. However, intermittent fasting isn’t necessarily a better way to lose weight than old-fashioned calorie cutting. 

A 2018 systematic review of several studies evaluating weight loss in overweight and obese patients found a weight loss of 0.8% to 13% of baseline weight without major adverse outcomes. Twelve studies comparing intermittent fasting to traditional calorie restriction found similar results. In 5 of the studies, blood sugar control was improved in subjects with type 2 diabetes.

Intermittent Fasting and Diabetes 

As mentioned above, time-restricted feeding may be advantageous to individuals with diabetes. A systematic review and meta-analysis of randomized controlled trials comparing the safety of IF with continuous calorie restriction on blood sugar control and weight was conducted. Both diets had similar effects on hemoglobin A1c and fasting blood sugar as well as improvements in lipid profiles, but IF was shown to have a better effect on weight loss.

A similar study also found that weight loss was superior with IF than with traditional calorie-controlled diets in individuals with type 2 diabetes. A meta-analysis of seven studies found that obese subjects lost more weight using IF than calorie-controlled diets. Blood sugar control was equivalent in both groups.

Intermittent Fasting and Age-Related Dementia

An area of study of particular interest to me is IF and age-related dementia. My mother suffers from dementia and prevention is key. While my mother’s condition is not reversible, I’ve been paying greater attention to my own eating patterns and risk factors. This includes eating at regular meal times, limiting added sugars, and not eating snacks after dinner. 

Since cardiovascular disease and dementia are associated with each other, reducing risk factors for cardiovascular disease could impact dementia risk. Fasting may be of benefit here.

A 4-week, randomized control trial of alternate-day fasting found improvements in cardiovascular markers, including reduced abdominal fat, lower LDL cholesterol, and reduced methionine- a pro-aging amino acid. A lower level of sICAM-1 (an age-associated inflammatory marker) was also noted. Alternate-day fasting appears safe in healthy individuals.

IF may aid in the prevention of vascular dementia as it helps reduce neuroinflammation, improves dyslipidemia in patients with Alzheimer’s disease, and protects against brain damage by controlling beta-hydroxybutyrate activity. It may also increase the creation of neurotrophic factors, which may improve mitochondrial function. Research also shows that fasting may improve synaptic activity in the hippocampus- the part of the brain involved in memory formation.

Fasting is Not for Everyone

While fasting does show promise in improving metabolic health, it is not advised for anyone with an eating disorder, a history of an eating disorder, or those at risk for eating disorders. In addition, fasting is not advised for pregnant or lactating women. The safety of fasting should be discussed with a physician, dietitian, or another healthcare provider.

Individuals with diabetes that take insulin should not go long periods of time without food due to the risk of hypoglycemia.

Fasting may help overweight or obese individuals. Blood sugar appears to be better controlled during fasting, as do other cardiovascular risk factors, including cholesterol, blood pressure, and waist circumference.

What Can I Eat During an Intermittent Fast?

One advantage of IF is that calories don’t need to be counted, but choosing nutritious food is still important. You can’t gorge on cupcakes for 8 hours and expect weight loss or improvements in blood sugar!

Below are a few ideas to get started if you would like to try intermittent fasting:

• Keep your dinner time to a reasonable hour. A recent study found that late-night dinners (10 PM) are associated with metabolic syndrome and weight gain.

• Eat breakfast if you are hungry first thing in the morning. An intermittent fast can be flexible. Most studies advise at least a 12-hour fast, including the 7 or 8 hours you sleep.

• Be mindful of snacking and overeating. Are you truly hungry, or is your snack a habit?

• Choose nutritious food! Include lean protein (chicken, eggs, fish) or plant-based protein (beans, lentils, tofu) at meals.

• Add lots of vegetables and fruit to meals for adequate fiber, phytochemicals, vitamins, and minerals.

• Use whole grains (rolled oats, 100% whole grain bread or cereals, brown rice, farro, quinoa) in place of refined grains.

• Limit alcohol and added sugar intake. Both contribute to weight gain and increased risk for chronic disease.

By Lisa Andrews, MEd, RD, LD

References:

1. Fasting | definition of fasting by Medical dictionary (thefreedictionary.com)

2. 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.

3. Harris L, Hamilton S, Azevedo LB, Olajide J, De Brún C, Waller G, Whittaker V, Sharp T, Lean M, Hankey C, Ells L. Intermittent fasting interventions for treatment of overweight and obesity in adults: a systematic review and meta-analysis. JBI Database System Rev Implement Rep. 2018 Feb;16(2):507-547. doi: 10.11124/JBISRIR-2016-003248. PMID: 29419624.

4. Wang X, Li Q, Liu Y, Jiang H, Chen W. Intermittent fasting versus continuous energy-restricted diet for patients with type 2 diabetes mellitus and metabolic syndrome for glycemic control: A systematic review and meta-analysis of randomized controlled trials. Diabetes Res Clin Pract. 2021 Sep;179:109003. doi: 10.1016/j.diabres.2021.109003. Epub 2021 Aug 12. PMID: 34391831.

5. Borgundvaag E, Mak J, Kramer CK. Metabolic Impact of Intermittent Fasting in Patients With Type 2 Diabetes Mellitus: A Systematic Review and Meta-analysis of Interventional Studies. J Clin Endocrinol Metab. 2021 Mar 8;106(3):902-911. doi: 10.1210/clinem/dgaa926. PMID: 33319233.

6. Stekovic S, Hofer SJ, Tripolt N, Aon MA, Royer P, Pein L, Stadler JT, Pendl T, Prietl B, Url J, Schroeder S, Tadic J, Eisenberg T, Magnes C, Stumpe M, Zuegner E, Bordag N, Riedl R, Schmidt A, Kolesnik E, Verheyen N, Springer A, Madl T, Sinner F, de Cabo R, Kroemer G, Obermayer-Pietsch B, Dengjel J, Sourij H, Pieber TR, Madeo F. Alternate Day Fasting Improves Physiological and Molecular Markers of Aging in Healthy, Non-obese Humans. Cell Metab. 2019 Sep 3;30(3):462-476.e6. doi: 10.1016/j.cmet.2019.07.016. Epub 2019 Aug 27. Erratum in: Cell Metab. 2020 Apr 7;31(4):878-881. PMID: 31471173.

7. Yoon G, Song J.   Intermittent Fasting: a Promising Approach for Preventing Vascular Dementia.   J Lipid Atheroscler. 2019 May;8(1):1-7.   https://doi.org/10.12997/jla.2019.8.1.1

8. Gu C, Brereton N, Schweitzer A, Cotter M, Duan D, Børsheim E, Wolfe RR, Pham LV, Polotsky VY, Jun JC. Metabolic Effects of Late Dinner in Healthy Volunteers-A Randomized Crossover Clinical Trial. J Clin Endocrinol Metab. 2020 Aug 1;105(8):2789–802. doi: 10.1210/clinem/dgaa354. PMID: 32525525; PMCID: PMC7337187.

More articles on fasting: