IF is a type of eating plan that involves limiting the time period when you eat. There are several different ways to do that, including:
- Restricting eating during a certain time of day
- Limiting the number of calories during a fasting period
- Rotating between normal eating days and fasting days
History of Diabetes and Intermittent Fasting
Fasting has been around for a long time: It has been a historical part of some spiritual traditions stretching back centuries. More recently, IF has been used as part of a healthy diet for weight loss, as a “detoxifying” strategy, and more.
Glucose Metabolism
To understand the benefits of intermittent fasting and diabetes, it’s important to know a little about how your body processes glucose and insulin.
Insulin is a hormone that enables glucose (sugar) to enter muscle, fat, and liver cells, where it’s used for energy. Normally, when blood glucose rises, the pancreas releases insulin. Insulin lowers blood sugar by “unlocking” cells so that they absorb sugar from the bloodstream. That’s how your body keeps blood sugar at a healthy level (between 70 to 99 milligrams/decilitre).
Insulin Resistance
Sometimes muscle, fat, and liver cells don’t respond normally to insulin. Glucose builds up in the blood because it can’t enter the cells. This is called insulin resistance because the cells resist the effects of insulin.
The pancreas responds by making more insulin. The extra insulin may keep the blood sugar level in a healthy range—until the pancreas can no longer make enough insulin to overcome the insulin resistance of the cells
Prediabetes means your blood glucose levels are higher than normal, but not high enough to qualify as diabetes. You may have prediabetes if you have insulin resistance. Prediabetes can also happen if your pancreas doesn’t make enough insulin to keep your blood sugar within the normal range.
Over time, prediabetes often progresses into type 2 diabetes.
How Intermittent Fasting Works
The primary goal of intermittent fasting for weight loss is to get insulin levels low enough so your body burns stored fat (instead of sugar) for energy.
Here is how it works: When your body breaks down the food you eat, it ends up as molecules in your bloodstream. One such molecule is glucose. It comes from the breakdown of carbohydrates.
Your body makes insulin so your cells can store and use that glucose. If you have more blood glucose than your body can use, it gets stored as fat for future use.
When you’re not eating meals or snacks, insulin levels drop. When insulin levels are low, fat cells release some of the stored fat so it can be used for energy. That results in weight loss.
Benefits of Intermittent Fasting
A few small studies have shown that intermittent fasting can have health benefits for people with diabetes, including:5
- Weight loss
- Lowering insulin requirements
A long-term study published in the New England Journal of Medicine showed that fasting can:6
- Lessen inflammation
- Lower insulin levels
- Improve a wide range of illnesses such as asthma, arthritis, and more
- Detox the body
- Help the body rid itself of damaged cells, which may lower the risk of cancer
Other reported benefits of fasting include:
- Lower triglycerides and LDL (“bad”) cholesterol levels
- Lower blood pressure
Side Effects
Intermittent fasting is safe for most people, but it isn’t right for everyone. IF diets may not be safe for people who are pregnant or breastfeeding, under age 18, have a history of eating disorders, or have diabetes.8
Fasting does have some downsides. Side effects of IF diets can include:
- Bad breath (which often results from low-carb diets)
- Trouble concentrating
- Excessive hunger
- Irritability
- Insomnia
- Headaches
- Dehydration
- Daytime sleepiness
- Low energy levels that may impact your ability to exercise, which is important for people with diabetes
- A much higher risk of low blood sugar (hypoglycemia)
- High blood sugar (hyperglycemia), if the liver responds to fasting by releasing stored glucose9
More research is needed to understand how common and how severe these side effects could be. Check with your healthcare provider before making major changes to your diet if you have diabetes.
Some side effects, like hyperglycemia or hypoglycemia, could be dangerous for people with diabetes. Talk to your healthcare provider before you start any type of IF diet.
Types of Intermittent Fasting Diets for Diabetes
Several Intermittent Fasting diets have proven safe and effective for people with diabetes. Here’s a look at the research.
The 5:2 Diet
The popular 5:2 diet was introduced in Dr. Jason Fung’s best-selling book “The Obesity Code” in 2016.4 It involves eating a recommended amount of calories five days per week, with two non-consecutive days of eating a reduced-calorie diet. On fasting days, you don’t stop eating altogether—you just reduce the number of calories.
If you have diabetes and want to try the 5:2 diet, speak to your healthcare provider or diabetes team. They’ll help you set a target calorie intake for the fasting and non-fasting days.
Studies on the 5:2 Diet
Studies have shown that the 5:2 diet may lower insulin resistance. It may also help with weight loss in people with type 2 diabetes or prediabetes.
The first long-term study of the 5:2 diet was published in 2018 by the Journal of the American Medical Association (JAMA). It found that fasting could be effective for those with diabetes who have trouble sticking to a long-term, daily diet regimen.10
The study tracked 137 people with type 2 diabetes:
- Half of them followed the 5:2 diet. They fasted for two non-consecutive days per week, taking in 500 to 600 calories on the fasting days. They ate normally on the other five days.
- The other half ate a daily restricted diet of 1200 to 1500 calories per day.
The study found that those who followed the 5:2 diet were just as likely to control their blood sugar levels as those on the daily restricted-calorie diet. Researchers said the 5:2 diet “may be superior to continuous energy restriction for weight reduction.”10
Safety of the 5:2 Diet
Some experts question the safety of the 5:2 diet for people with diabetes. However, a long-term study published in 2018 reported that “fasting is safe for those with diet-controlled type 2 diabetes.”
This study found the 5:2 diet safe for those with diabetes. Still, it’s important to talk to your healthcare provider before fasting or starting any other type of diet.
Early Time-Restricted Feeding Diet (eTRF)
With an early time-restricted feeding (eTRF) diet, you fit all your meals into a specific period of time each day.
The eTRF diet plan may be an eight-hour, 10-hour, or even a six-hour plan. On the eight-hour plan, if you begin eating at 7:00 a.m., the last meal or snack for the day would be at 3:00 p.m. An example of the 12-hour early time-restricted feeding plan would be when you eat the first meal of the day at 7:00 a.m. and the last meal or snack no later than 7:00 p.m.
How the eTRF Diet Works
The eTRF diet may work with your circadian rhythm. This is the body’s internal clock, which controls the timing of sleep, waking, and metabolism. That’s why some think the diet could aid weight loss.11
If you stop eating earlier in the evening, you will extend your overnight fast. According to a study published in the New England Journal of Medicine, fasting triggers some important cell functions, such as lowering blood sugar and boosting metabolism.
Benefits of the eTRF
Benefits of the eTRF diet include:
- Less appetite
- Weight loss
- More fat loss via oxidation (burning of fat)12
- Lower blood pressure
Study on the eTRF Diet for Diabetes
In a 2018 study, the eight-hour eTRF diet was compared with the 12-hour diet. The study found that the eight-hour group had dramatically lower insulin levels than the 12-hour group. Both groups maintained their weight. And both groups lowered insulin and blood pressure.
Safe Ways to Do Intermittent Fasting With Diabetes
Follow these tips if you have diabetes and plan to start an IF diet:9
- Consult with your diabetes team about whether the diet is a good choice for you. Follow their advice on any changes to your medication schedule. You want to be sure to keep a healthy blood glucose level.
- Test your blood glucose levels often.
- If you have symptoms of hypoglycemia, break the fast immediately. Use your action plan, such as taking glucose tablets followed by a snack. Talk to your healthcare provider before resuming the fast.
- If you have type 1 diabetes, watch for signs of hyperglycemia when you fast. These include fatigue, extreme thirst, and frequent urination. Contact your healthcare provider right away if you have these symptoms or your blood sugar level stays high.
Meal Planning Tips
As with any eating plan, it’s important to maintain a balanced diet to ensure your body is getting the nutrition it needs for long-term health. Include these meal-planning tips in your IF plan:
- Include foods from all of the food groups to get adequate fiber, protein, vitamins, and minerals.
- Eat foods that fill you up and keep your blood sugar steady during the fast, such as lean protein (fish, seafood, poultry), beans, nuts, fruits, vegetables, and fresh salads.
- Don’t overeat during the non-fasting periods.
- Just before you fast, eat foods that are more slowly absorbed, including foods that are lower on the glycemic index scale: carrots, dark leafy greens, non-starchy vegetables, most fruits, beans, oatmeal, bran cereals, quinoa, barley, nuts, milk, and yogurt.14 These foods are often high in fiber or protein and are digested slowly.
- When you break the fast, limit the amount of fatty and sugary foods you eat. Instead of frying, try grilling or baking chicken or fish; choose fresh fruit instead of ice cream, bakery items, and candy.
- Drink lots of fluids (mostly water) during the fast to avoid dehydration. Avoid sugary drinks.
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