Intermittent fasting has a lot of promise for weight loss - partly because the fasting itself has beneficial effects, and partly because it’s just an easier way of reducing calories without having to count and measure and track. “Eat only between noon and 7pm” is a whole lot easier to manage than “eat 1500 calories per day.”
But what about metabolic problems that are related to weight gain but not quite the same? Here’s a look at intermittent fasting and type 2 diabetes (T2D) - does it help protect people at risk from developing the disease, and is it safe for people who are already diabetic?
1. There’s quite a bit of evidence in favor.
Intermittent fasting has been studied pretty extensively for weight loss, but there are also some studies specifically on people with T2D. For example, this study explored an IF (4-8 hour feeding window per day) intervention in 10 adults with Type 2 diabetes, focusing on whether or not the patients could put up with it and whether it was safe. And it turns out it worked pretty well: the patients had lower morning blood sugar during the IF intervention, and fewer blood sugar spikes after meals.
Another group of researchers compared IF (fasting 2 days/week) to ordinary calorie restriction for people with T2D. Their results showed that both diets delivered comparable improvements in blood sugar control and weight. And a review of multiple studies comparing regular calorie restriction to intermittent or alternate-day fasting confirmed the value of the IF/ADF approach for managing blood sugar.
For folks more interested in prevention than treatment, another study in overweight women at risk of developing T2D found that intermittent energy restriction (very low-calorie diet 2 days/week) and continuous calorie restriction (moderately low-calorie diet all the time) caused the same amount of weight loss, but the intermittent restriction improved insulin sensitivity more.
And here’s an interesting case report. A case report is basically the story of one individual patient. In this case, the guy spent 4 months on IF. His technique was to do a 24-hour fast three times a week, but over the 4 months of the study, he slowly lengthened the fasting period until he was fasting for nearly 2 full days twice a week. By the end, he’d dropped 17% of his body weight, dramatically improved his long-term blood sugar control, and gotten off all his meds. As the case report noted: “The patient did not find it difficult to adhere to the fasting schedule and did not experience any hypoglycaemic episodes or other significant adverse effects.”
How does it work? Partly, it’s just the calorie restriction, but the fasting itself also does have something to do with it. For example, this paper, in mice with obesity-induced diabetes, found that intermittent fasting improved survival of beta cells in the pancreas. Those are the cells that produce insulin, so by improving beta cell survival, IF helped the mice regulate insulin and blood sugar more tightly. Not a bad benefit for just...not eating.
2. Some studies suggest it may also alleviate secondary effects
Most of the studies above focused on blood sugar regulation and insulin sensitivity - which, after all, are the main issues that define diabetes. But other research indicates that intermittent fasting may also be helpful for other symptoms and consequences of T2D. For example, diabetic retinopathy (vision issues) may respond to IF, at least in mice. The researchers who did that study found that IF actually helped with diabetic retinopathy by modifying the gut biome. Specifically, IF increased the levels of certain beneficial bacterial species, which caused the mice to make more of a bile acid called tauroursodeoxycholate (TUDCA). TUDCA is neuroprotective and may have protected retinal cells in the eyes against damage. One commenter on the article noted that:
“As the TUDCA TGR5 receptors are present in neural cells, it is tempting to speculate that intermittent fasting could also have the potential to improve other diabetic microvascular complications, in particular diabetic neuropathy. The most important question, however, is whether and to what degree could such a concept be extrapolated to humans.”
3. Research on people taking meds: reason to be cautious
One major potential problem with IF is that people who take insulin or other drugs to manage diabetes might need to take special care in adjusting their medications. As this study found, patients on an intermittent fasting protocol did have a higher risk of hypoglycemic events, compared to patients on a standard calorie-reduced diet. Even when they reduced blood-sugar lowering medications, they still had an average of 1.4 hypoglycemic events over the 12-week study. The researchers did still confirm that fasting lowered fasting blood sugar and improved long-term blood sugar control, but this indicates that it might also have significant risks.
Another review describes medication changes required or tested for patients taking insulin and other hypoglycemic drugs. The study does describe the protocol in detail, but it’s really complicated and depends on regular, accurate blood sugar readings.
Basically, if you take blood sugar lowering meds, the Paleo approach to intermittent fasting is to talk to your doctor, the reasonable approach to intermittent fasting is to talk to your doctor, and the best approach to IF for weight loss is to talk to your doctor.
4. There are lots of schedule options.
The studies above used all kinds of protocols - from restricted feeding windows every day to two days a week of semi-fasting (~500 calories/day) to longer fasts of 1-2 full days. There are a lot of options and all of them seem to have some benefits.
Restricted feeding windows: this is when you set a certain amount of time every day to eat and fast for the rest of the day. Many people choose the afternoon and evening, but this study in patients with Type 2 Diabetes showed successful results with patients eating only breakfast and lunch (and then fasting during the late afternoon and evening).
One-day (24-ish hour) fasts: a few of the successful studies above used one or more full-day fasts per week (or “fasts” that involved only a few hundred calories on the “fast” day).
Longer fasts: This study even used a “fasting” protocol that involved 7 straight days of 300 calories/day, which is really stretching the limit of what you could consider “intermittent” or “fasting,” but they had great results with it in patients with type 2 diabetes, especially for blood pressure.
It almost seems like any kind of eating schedule that gets people to stop eating sometimes is pretty good for us - which is great, because then everyone can pick an eating pattern that works with their work schedule and preferences.