Healthy eating habits have always been important to controlling blood sugar. But when you eat could also play an increasingly important role. Fasting between meals has been one approach to restricting calories, but there has been limited research to examine health benefits until recently.
Newer research has studied intermittent fasting in people with Type 2 diabetes or prediabetes. While the results are mixed, some studies, including a recent review paper, have shown improvement in insulin sensitivity, blood sugar levels and weight loss — which is one of the biggest contributors to developing diabetes.
“The concern would be that people living with Type 1 diabetes are taking insulin, and so if they fast they would be more prone to having lower than normal blood sugar levels,” says Toby Smithson, a registered dietitian, certified diabetes care and education specialist and founder of DiabetesEveryDay, an online resource dedicated to helping patients successfully manage diabetes.
What Is Intermittent Fasting?
The typical American diet consists of three meals a day plus snacking in between meals. “When people are eating all day and not exercising, they are getting their energy from those calories and not burning their stored fat,” says Mark Mattson, a neuroscientist at Johns Hopkins University in Baltimore.
In contrast, intermittent fasting is about eating during a specific time period. That means eating for a certain number of hours each day and fasting for the remainder of the day. The goal of intermittent fasting for those with diabetes is to fuel the body’s energy by burning fat stores and to lose extra weight, improve insulin sensitivity and lower blood sugar levels.
The other result of intermittent fasting is called metabolic switching. This happens when the body, after hours without food, exhausts its blood glucose stores and switches over to start burning fat.
There are two main sources of energy in the body — blood glucose in the liver and ketones made from the breakdown of fats. “It usually takes about 10 to 12 hours to deplete the glucose in the liver and start burning fat as the energy source,” says Mattson, who has studied intermittent fasting for the past 25 years. “Intermittent fasting can trigger that metabolic switch.”
Types of Fasting
There are different fasting schedules to consider — all focused on when to eat and when to fast. Some fasting regimens are rather simple — it could mean skipping breakfast and eating an early lunch and dinner.
Other fasting routines are more restrictive and limit eating after a specific time of day, usually at nighttime. Some fasting regimens rotate between eating normally on certain days of the week and fasting one or two days a week. On the extreme end, some fasts last over several days — and even weeks. However, people do not have to resort to extreme fasts to see positive results, says Smithson, author of “Diabetes Meal Planning and Nutrition for Dummies.”
Benefits of Fasting
There is a lack of extensive research examining the benefits of intermittent fasting among people living with diabetes. The first studies looking at intermittent fasting in diabetes started about a decade ago, and more recently researchers have begun to include people with prediabetes and Type 2 diabetes in studies. Most doctors still consider fasting somewhat experimental.
In a review paper of current research, published in the New England Journal of Medicine, Mattson noted a number of health benefits connected to intermittent fasting. “Many things happen during intermittent fasting that can protect organs against chronic diseases like Type 2 diabetes, heart disease, age-related neurodegenerative disorders, even inflammatory bowel disease and many cancers,” he says.
In addition, a few recent studies took a closer look at fasting in people with diabetes and showed mild health benefits:
— A Canadian study that followed three people with Type 2 diabetes found that fasting led to several health benefits, including: weight loss, improved blood sugar control, improvement in insulin resistance and elimination of the need for insulin therapy.
— Researchers studied 19 people with metabolic syndrome, a cluster of conditions that increase the risk of diabetes, heart disease and stroke. The study, conducted at the University of California, San Diego, found reductions in body weight when people ate within a 10-hour window over a 12-week period.
— Another study examined two groups of four men each with prediabetes — the fasting group ate over a six-hour period and another group ate over a 12-hour period. Even though the five-week study did not show improvement in blood sugar levels or weight loss in the fasting group, there was an improvement in lowered insulin, improved insulin sensitivity and blood pressure.
On the other hand, an alternate-day fasting regimen did not result in major benefits compared to calorie restriction without fasting, according to a 2017 study published in JAMA. One hundred women and men with obesity were followed for four years and randomized to be included one of three groups: alternate day fasting, calorie restriction or no intervention. The researchers at the University of Illinois in Chicago found that there were no major differences between the fasting and calorie restriction groups in terms of improving blood pressure, heart rate, blood sugar levels, fasting insulin or insulin resistance.
Challenges While Fasting
Even with new research showing some health benefits of intermittent fasting, there are still many ingrained hurdles to greater adoption of intermittent fasting into people’s eating habits, says Mattson. “The abundance of food and extensive marketing are major hurdles to overcome.”
There are several challenges to switching to an intermittent fasting plan to be aware of, including:
—Hunger.Changing your eating schedule is not easy and will not happen overnight. “Many people will be hungry and feel irritable,” says Mattson. The good news, he says, is that these feelings of hunger usually disappear within several weeks to a month.
—Dehydration. Be on alert for dehydration from fasting. This can result pretty quickly if you limit your food and beverage intake, or if you’re physically active, in hot weather or perspiring a lot, says Smithson. It’s encouraged to drink water, coffee, tea or zero-calorie drinks when you’re fasting. “When you become dehydrated, you also may see higher blood sugar readings, so make sure to check your readings regularly.”
—Lack of concentration. At first, adjusting to a new eating schedule may cause a reduced ability to concentrate during periods of food restriction.
— Starvation. For those eager to fast for longer periods of time over 24 or 72 hours, be sure to watch for signs of starvation, which could be dangerous for your health. Going too long without eating may actually encourage your body to start storing more fat to react to starvation.
Before You Fast
Research shows that intermittent fasting is safe and can be continued indefinitely for people with prediabetes and Type 2 diabetes. But intermittent fasting is not an option for those with a history of eating disorders, children and teens under age 18, women who are pregnant and those living with Type 1 diabetes.
If you’re considering following a fasting program, be sure to talk to your doctor or a registered dietitian about your goals.
Once you start an intermittent fasting program, always check and re-check your blood sugar levels, says Smithson. “Whether it’s with a blood glucose meter or a continuous glucose monitoring system, it’s recommended to check your blood sugar levels at least three times a day — even more so if you’re fasting.”
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