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Intermittent Fasting Works For Weight Loss. But Is It Safe If You Have Diabetes?

Intermittent Fasting Works For Weight Loss. But Is It Safe If You Have Diabetes?

The intermittent fasting trend is already a few years old and shows no sign of slowing down. Both research studies and tons of anecdotal evidence support it for weight loss and several other potential health benefits. But if you’re one of the approximately 35 million Americans with type 2 diabetes (and one of the 1.6 million with type 1 diabetes), is it safe to do intermittent fasting? After all, when you fast, doesn’t that pose a risk for hypoglycemia (low blood sugar)? 

The short answer is: it depends. 

There are a few important factors when it comes to intermittent fasting and diabetes:

  • The type of fast
  • The length of the fast
  • Medication(s) taken

Fasting Risks Associated With Diabetes

Indeed, hypoglycemia is the biggest risk for people with diabetes who fast. But hyperglycemia is a risk as well. This is especially true if somebody cuts back on their diabetes medication and takes insulin. Why would somebody cut back on their medication if they take insulin? To avoid hypoglycemia. 

But the delicate dance of managing diabetes while fasting doesn’t end there. If you cut back too much on your medication, then your blood sugar levels will be too high. Diabetic ketoacidosis is also a potential danger. So, too, is dehydration.

In light of these risks, should you avoid intermittent fasting altogether? 

Not necessarily. 

In most instances, dangerously-high or low-blood glucose levels can be avoided with a sensible fasting strategy.  And if you have diabetes and are considering doing intermittent fast, don’t go it alone. Consult with your physician or other health professional. 

Different Fasting Methods

There are several different types of fasting. There’s daily time-restricted feeding, which limits intake of calories to a defined window. Fasting for 16 hours a day has become one of the most popular methods. One study suggests that an early time-restricted feeding pattern (ending the calorie-consumption window by early afternoon) improves blood sugar levels, and insulin signaling. However, the study excluded people with diabetes. 

Other forms of fasting include 5:2 (eating normally five days a week and restricting calories the other two days); alternate day intermittent fasting; doing a 24-hour fast one day a week, etc. 

Diabetes and Dehydration with Intermittent Fasting

Martin M. Grajower, MD, is a clinical professor in the Department of Medicine (Endocrinology) at Albert Einstein College of Medicine, New York. 

Grajower, who did his fellowship under Dr. Harold Rifkin, co-author of the seminal textbook on diabetes, Diabetes Mellitus: Theory and Practice, says in an article on the National Institute of Diabetes and Digestive and Kidney Diseases (under the auspices of the National Institute of Health) website, the risk of dehydration is low with intermittent fasting (time-restricted feeding) because fluid intake is not restricted (as long as it’s non-caloric during the fasting window). 

How do the newest class of diabetes drugs affect the risk of dehydration? So-called SGLT-2 drugs (Sodium-glucose co-transporter 2 inhibitors; gliflozin) were introduced to the market in 2013, and work by reducing the absorption of glucose via the kidneys; excess glucose is excreted through urination. 

Grajower says that besides lowering blood sugar, these drugs act as diuretics. Thus, practitioners (and the patient) should be aware of the fact that both these actions must be considered when adjusting the dosages. Grajower suggests stopping the usage of SGLT-2 two days before beginning a fast because of the dehydration aspect.

Fasting For Religious Holidays Or Surgery

This isn’t necessarily the case with daily, time-restricted feeding (which should be done at the same time every day to regulate blood sugar levels). Rather, this is more so the case with religious observance 24-hour fasts (Yom Kippur, Ramada) or because of surgery. 

If you’re thinking about fasting in the near future for 24 hours because of a holiday or you require surgery, Grajower, in this article, suggests the following:

  • Insulin-increasing drugs known as Sulfonylureas should be stopped 36 hours before a fast commences. 
  • Glucose-regulating drugs that are taken with meals (glinide drugs such as Meglitinide and Nateglinide) should be avoided with a 24-hour fast or a zero-carbohydrate meal.
  • For those taking insulin drugs, long-lasting medications can last almost two days. Therefore, the dosage should be reduced both two days and one day prior to a 24-hour fast; older and other insulin drugs don’t last as long so the dosage the day before the procedure needs to be adjusted.
  • Although Metformin, pioglitazone, and DPP-4 inhibitors rarely cause hypoglycemia, do not take them on the day of a 24-hour fast.
  • Monitor blood-glucose levels more often than usual on the day of a 24-hour fast.

What is the Best Fasting Method If You Have Diabetes?

Although Grajower doesn’t recommend one method of fasting over another in the article, it seems that a time-restricted feeding window of, beginning with, 12 hours makes the most sense. Ideally, the fasting window would begin by the early-to-middle-evening hours (finish eating by 7 or 8 p.m.). If there are no problems, after one week of a successful 12-hour fast, you can increase your fasting window for another hour, for another week, gradually building up to a 16-hour fast. 

Again, do not start an intermittent fasting regimen without first getting approval from your doctor. If you have type 1 diabetes, this puts you at greater risk of fasting side effects. 


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