Most fad diets don’t live up to the hype, let alone undergo rigorous scientific scrutiny. But intermittent fasting seems to be the exception. These programs involve skipping high-calorie foods or drinks for long periods of time – anywhere from 16 hours to a few days – and they’re growing in popularity. Studies have also found them to be effective for weight loss.
Doctors often recommend weight loss for people with type 2 diabetes, which may have beneficial effects on blood sugar and insulin sensitivity as well as disease progression. For this and other reasons, experts are actively studying the effects of intermittent fasting on people with type 2 diabetes. However, there are some safety concerns. “People with diabetes should be the ones who benefit the most from intermittent fasting,” says Benjamin Horn, director of cardiovascular and genetic epidemiology at Intermountain Healthcare in Utah. “But there are also some of the biggest potential safety concerns with these diets because of the medications that people with diabetes typically take.”
Horn recently co-authored several papers on the effects of intermittent fasting on people with diabetes. One of them appears in the 2020 issue of JAMA and looks specifically at the risk profile of these practices. “It’s very easy to start an intermittent fasting regimen on your own, so when you’ve got a diabetes treatment plan in place, our main concern is the safety issues around fasting,” he says. Based on his work and that of others, Horn says that for most people with type 2 diabetes – especially those who don’t take medications to control their blood sugar – research suggests that intermittent fasting is both safe and potentially beneficial. However, intermittent fasting isn’t for everyone. Here, Horn and other experts explain the possible risks of an intermittent fasting program, as well as the benefits and best ways to do it.
Risks of intermittent fasting
Hypoglycemia, also known as hypoglycemia, can cause a rapid heart rate, sweating, shaking and other symptoms. If severe, it can lead to weakness, seizures, and even death. The increased risk of hypoglycemia in people with type 2 diabetes – especially if they go for long periods without eating – is one of the first dangers experts consider when evaluating the safety of intermittent fasting. “If you’re taking medications designed to reduce the amount of glucose in your blood, coupled with fasting, these medications can lead to potentially fatal hypoglycemia,” Horn said. “It’s not a minor safety risk.”
For a 2018 study in the Journal of Diabetic Medicine, researchers in New Zealand found that the incidence of hypoglycemia did increase in people with type 2 diabetes who tried intermittent fasting. However, this increase was consistent with the results of other weight loss diets, including traditional approaches that encourage people to consume fewer calories per day. In addition, the people in the study were taking medications designed to lower blood sugar. “It’s the medication that causes hypoglycemia, not the diet itself,” said study author Brian-Corley, a diabetes specialist with the New Zealand Capital and Coastal District Health Authority. Corley said people taking these medications can reduce the risk of dangerous blood sugar drops by working closely with their doctors, monitoring their blood sugar more carefully on fast days and educating themselves on how to manage hypoglycemic events. In other words, an intermittent fasting program isn’t necessarily right for these patients. They just need a little more care. Also, his study found that intermittent fasting helped reduce weight and improve fasting glucose, hemoglobin A1C and overall quality of life.
For people who don’t take medications to lower their blood sugar, Horn says the risk of hypoglycemia appears to be very low. “People should still consult someone who treats diabetes – a doctor such as an endocrinologist, or at least a dietitian trained in diabetes treatment,” he says. Like Coley, he says even people taking blood sugar medications can try intermittent fasting, as long as they work with a specialist. “They should or shouldn’t not be that much. It’s more important that they should be monitored,” he says. (This doesn’t apply to people with type 1 diabetes; Horn says intermittent fasting is too risky for this group.)
In addition to hypoglycemia, the second major problem is dehydration. High blood sugar leads to general dehydration, and people with type 2 diabetes are already at elevated risk. If people are drinking or eating below normal levels, intermittent fasting may further increase these risks. (Food has been shown to provide one-third or more of the water people consume each day.)
Benefits of intermittent fasting
While intermittent fasting may pose risks for some people, it can also provide benefits that go beyond other methods. A 2017 study in the World Journal of Diabetes found that just two weeks of intermittent fasting resulted in significant weight loss (averaging more than 3 pounds) and improved blood sugar levels. “Intermittent fasting may lead to reduced insulin resistance,” said Kerry Mansell, co-author of the study and a professor at the University of Saskatchewan School of Pharmacy and Nutrition in Canada.
Research supports this hypothesis. Some studies of people with diabetes have found that intermittent fasting may increase insulin sensitivity and lower insulin levels in the blood. That’s a big problem. “Essentially, fasting is doing what we prescribe for diabetes medications, which is to increase insulin sensitivity,” Horn says. At least one small trial (just three people) found that using an intermittent fasting diet allowed people with diabetes to stop taking their insulin medications altogether. The results of that study still need to be replicated in a larger group. However, the results are encouraging. Insulin resistance is associated with higher levels of inflammation and other risk factors for cardiovascular disease. “Even when people didn’t lose weight through a fasting regimen, some studies found significantly higher insulin sensitivity,” Horn said. “That’s something you don’t typically see on other calorie-restricted diets.”
How does fasting produce these benefits? There are a number of theories, some of which may prove to be correct. One major hypothesis – which has been supported by solid research – is that fasting initiates a cell-cleansing process that removes old or unhealthy cells and allows new ones to thrive. Based on this work, some experts believe that the human body is not designed for the modern dietary environment and its three-meal-a-day plus snacking diet plan. Intermittent fasting, they say, may be more similar to the way humans have eaten for most of our species’ history.
More work needs to be done to eliminate it all. But research to date suggests that intermittent fasting may provide unique and meaningful health improvements for people with type 2 diabetes.
Which fasting plan is best?
The term intermittent fasting does not refer to a clearly defined practice. Several different approaches fall under the umbrella of intermittent fasting. The three most common and well-researched approaches are known as time-restricted eating, alternate-day fasting, and the 5:2 diet.
The first of these – time-restricted eating – involves compressing all of your calories for the day into a six- to eight-hour “feeding window. For example, a person on this diet might eat between noon and 6 p.m. Each day, and for the other 18 hours of the day, avoid all high-calorie foods and beverages. Meanwhile, people who fast every other day eat normally one day, but consume few or no calories the next. Finally, the 5:2 diet consists of eating normally five days a week but fasting the other two days.
There are many variants of each of these plans. At this point, it’s unclear which of them, if any, is best for people with type 2 diabetes. “I think a time-restricted diet is probably the most common, followed by a two-day-a-week fast,” Horn says. “But at this point, I’d say no one plan stands out as the best option.” The “right” plan, he adds, is the one that patients will stick to. Even if a more intense fasting program proves to be the most beneficial, it doesn’t matter if people can’t stick to it.
How to start intermittent fasting
The first step is always to talk to your doctor or care team. They should be able to help you weigh the benefits and risks, identify ways to avoid nutritional deficiencies in your diet, and adjust any medications you’re taking if necessary to avoid problems. “Safety must come first,” says Horn.
But don’t be surprised if your health care provider isn’t keen on fasting. These programs are still relatively new and are not usually taught in medical schools. “People may encounter resistance, or their physicians may be less familiar with these programs,” says Horn. If your doctor says fasting isn’t right for you, that’s one thing. But if she or he seems dismissive of fasting diets in general, it may be worth seeking a second opinion from a provider who has experience with these programs.
Intermittent fasting may be risky for some people. But there is now evidence that it may be a valid alternative, or even a better alternative, to the classic weight loss program for people with type 2 diabetes.
