Intermittent fasting is a practice that is gaining medical acceptance for improving various health parameters. This article provides an overview of the potential health benefits and special considerations for patients with diabetes. Please consult your healthcare provider to discuss your individual circumstances to determine whether intermittent fasting may be right for you and how to approach it safely.

What Is Intermittent Fasting (IF)?

Intermittent fasting (IF) is defined as a specific time period of not eating or drinking caloric beverages (typically for a minimum of 16 hours). IF may be done on daily basis (e.g., only consuming calories between the hours of 12 pm and 6 pm every day) or less frequently (e.g., fasting for 16-24 hours once or twice per week). Longer fasting periods that span for several days or more are usually referred to as periodic fasting, as opposed to intermittent. Unlike periodic fasting, IF carries a minimal risk for malnutrition, which can be a health concern associated with longer fasting periods.

What Are the Health Benefits of IF?

Overeating, which is a common issue in the United States today, can contribute to a variety of health issues, including insulin resistance and overweight and obesity. Researchers note that

Because animals, including humans, evolved in environments where food was relatively scarce, they developed numerous adaptations that enabled them to function at a high level, both physically and cognitively, when in a food-deprived/fasted state.

Moreover, a considerable volume of research has demonstrated than intermittent fasting appears to confer a variety of health benefits, in particular on various metabolic parameters. Some potential benefits in human subjects that are highlighted in the scientific literature include:

Weight loss and maintenance

Reduced inflammation

Improved insulin sensitivity

Improved blood glucose levels

Improved cardiovascular parameters, including serum cholesterol and triglyceride reduction

In addition, animal studies indicate that IF may positively modulate various disease processes, including:

Type 2 diabetes

Cardiovascular disease

Various neurological disorders (including models of Alzheimer’s, Parkinson’s and Huntington’s disease)

Cancer

Excitingly, recent small-scale human clinician trials of IF in patients with multiple sclerosis and cancer have yielded very promising results. However, more well-controlled clinical studies in human subjects are needed to further elucidate the relevance of these findings and the abundant data from animal model studies when it comes to the modulation of these specific health disorders.

Keep in mind that IF may not be safe for everyone. For instance, pregnant women and those with certain health conditions or taking medications that may promote electrolyte imbalances may be discouraged from the practice. Be sure to consult your healthcare provider to decide whether fasting is a safe choice for you.

Important Considerations for People with Diabetes

For people with diabetes, intermittent fasting may be of particular benefit, in improving insulin resistance and helping to maintain stable blood glucose levels over extended periods of time. However, it is very important for people with diabetes to plan ahead and be aware of how fasting may affect their medication doses (insulin and/or other antihyperglycemic medications). For patients who use insulin, it is important that the basal dose or rate is properly set to maintain blood glucose stability in the absence of food, as the primary concern of fasting for patients with diabetes is hypoglycemia (low blood sugar).

It is recommended to discuss IF in the context of glycemic control and medication adjustments with a knowledgeable healthcare provider prior to attempting IF. It is particularly important to monitor blood glucose levels more closely and treat any out of range blood sugar levels appropriately. Patients are also encouraged to maintain adequate hydration by consuming appropriate among of non-caloric beverages (e.g., water).

The following subsections provide a basic overview of IF with type 1 diabetes and type 2 diabetes but are not intended to substitute for the individualized medical advice of a healthcare provider.

In general, patients with type 1 diabetes are typically instructed by their healthcare provider to omit any fast-acting insulin doses that they would take for meals or snacks (an exception would be a correction dose in the instance of hyperglycemia). They may be instructed to reduce their basal insulin dose or rate to accommodate the expected increase in insulin sensitivity due to fasting. The specific change in the basal dose or rate may depend on whether they use an insulin pump or injection therapy with long-acting insulin, and also the particular type of long-acting insulin that is used.

Some practitioners may be very cautious about preventing hypoglycemia and counsel patients to reduce their long-acting insulin dose by as much as 30-50%. In general, if basal testing is performed frequently, and the basal insulin therapy is well-set to maintain stable blood glucose levels in the absence of food or exercise, patients will not typically experience a need for such a drastic decrease from a short fast. In any case, it is imperative to pay close attention to blood glucose levels and make small corrections, as appropriate.

In the case of hypoglycemia, patients should correct the blood glucose levels promptly with fast-acting carbohydrates (e.g., glucose).

In general, for patients with type 2 diabetes who use insulin, the recommendations for insulin dose changes are similar to those discussed above for those with type 1 diabetes. Healthcare providers may also instruct patients to adjust medication doses of other antihyperglycemic agents (e.g., oral medications).

In general, other drugs carry a lot lower risk for hypoglycemia during fasting than does insulin. Two prominent exceptions are sulfonylureas and meglitinides, so patients may be instructed to omit these medications when fasting. Also, those on SGLT-2 inhibitors may be instructed to withhold these during a fast, in particular, if there is any concern with whether the patient is adequately hydrated.

Conclusions

Intermitted fasting appears to confer numerous potential health benefits and may be carried out safely in patients with diabetes with the guidance of an experienced healthcare provider. Those with diabetes should discuss medication adjustments with their medical team, and take particular care to stay hydrated and monitor their blood glucose levels closely during and following IF.

References

Arnason TG, Bowen M, Mansell KD; “Effects of intermittent fasting on health markers in those with type 2 diabetes: A pilot study” (2017) World Journal of Diabetes 8(4): 154-164. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5394735/

Furmli S, Elmasry R, Ramos M, Fung J; “Therapeutic use of intermittent fasting for people with type 2 diabetes as an alternative to insulin” (2018) BMJ Case Reports https://casereports.bmj.com/content/2018/bcr-2017-221854.full

Grajower MM and Horne BD; “Clinical Management of Intermittent Fasting in Patients with Diabetes Mellitus” (2019) Nutrients 11(4): 873. https://www.mdpi.com/2072-6643/11/4/873/htm

Horne BD, Muhlestein JB, Anderson JL; “Health effects of intermittent fasting: hormesis or harm? (2015) The American Journal of Clinical Nutrition 102(2): 464-470. https://academic.oup.com/ajcn/article/102/2/464/4564588

Mattson MP, Longo VD, Harvie M; “Impact of intermittent fasting on health and disease processes.” (2017) Ageing Research Reviews 39: 46-58. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5411330/

Patterson RE and Sears DD: “Metabolic Effects of Intermittent Fasting” (2017) Annual Review in Nutrition 37: 371-393. https://www.annualreviews.org/doi/pdf/10.1146/annurev-nutr-071816-064634

Read more about blood glucose monitoring, diabetes management, insulin.