Diabetes and Intermittent Fasting
- April 02, 2021
Intermittent fasting is a type of eating plan that involves a limited time period when caloric intake is restricted. This can vary from fasting (not eating at all) all day long for several days per week, to simply limiting the number of calories that are ingested during the fasting period. There are specific intermittent fasting diets, such as those that restrict food intake after a specific time of day (usually during the evening hours), to those that rotate between eating normally and restricting a certain number of calories during the day on fasting days. More dramatic fasting diets involve restricting all foods for a complete 24-hour time span, or longer.
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Fasting has been around for some time, particularly if you consider the historical role of fasting as part of many types of spiritual rituals. More recently, intermittent fasting has been used as part of a healthy diet for weight loss, as part of “detoxifying” the body, and more. But there has been much controversy surrounding the topic of fasting for those with diabetes.
Today, there is a growing body of evidence indicating that specific types of intermittent fasting diets may be beneficial for people with diabetes. In addition, scientists are beginning to speculate that when a person fasts may be just as important as the diet itself.
To fully understand the benefits of intermittent fasting and diabetes, it’s important to know a little about the physiology of the body when it comes to the action of glucose and insulin.
Insulin is a hormone that enables glucose (sugar)—derived from the food we eat—to enter the cells of muscles, stored fat, and the liver, where it is used for energy. When blood glucose levels rise, insulin is released from the pancreas; the insulin lowers blood sugar levels as it carries the glucose into the cell, keeping blood sugar levels within normal levels.
When the cells of the muscles, fat, and liver are unable to respond normally to insulin, glucose begins to accumulate in the blood because it is not able to properly enter the cells. This is called insulin resistance. When insulin resistance begins, the pancreas will attempt to make more insulin, to overcome the condition (in an effort to transport the blood sugar into the cells). The blood sugar level will stay within normal range until the pancreas is no longer able to make enough insulin to combat the weakness of the cells.
When blood glucose levels are higher than normal, but not high enough to warrant a diagnosis of diabetes, it’s called prediabetes. Prediabetes usually occurs in those with some level of insulin resistance. Prediabetes also occurs in those whose pancreas doesn’t make enough insulin to keep the blood sugar within the normal range. Over time, prediabetes often progresses into type 2 diabetes.
The primary goal of intermittent fasting for weight loss is to get the insulin levels to decrease to a level where the body will begin to burn stored fat for energy.
Here is how it works. When the food we eat is metabolized (broken down to be used as energy in the body), it ends up as molecules in the blood stream. One such molecule is glucose (which comes from the breakdown of carbohydrates). Normally, when there is more circulating blood glucose than the body can use for energy, the excess is stored as fat for future use. But, for glucose to be utilized by the cells, it requires insulin. Between meals the body doesn’t require insulin (unless a person is snacking) so insulin levels decline. When insulin levels are low, the fat cells release some of the stored glucose, resulting in weight loss.
A few small human studies have shown evidence that intermittent fasting can have health benefits for those with diabetes. These include:
- Weight loss
- Lowering insulin requirements
A long-term study, published in the New England Journal of Medicine, revealed that a fasting state can support several benefits including:
- Lessening inflammation
- Lowering insulin levels
- Improving a wide range of illnesses (including asthma, arthritis, and more).
- Detoxifying the body
- Helping the body rid itself of damaged cells (which may lower the risk of cancer)
Other reported benefits from fasting include:
- Lowering cholesterol levels (specifically triglycerides and LDL cholesterol)
- Reducing blood pressure
According to a 2019 study published in the journal Nutrients, “Long-term benefits of fasting, including cardiovascular risk reduction, remain to be fully studied and elucidated, especially in humans.”
Side effects of intermittent fasting may include:
- Bad breath (which often results from low carbohydrate diets)
- Difficulty concentrating
- Excessive hunger
- Sleepiness during the day
- Low energy levels (may impact a person’s ability to exercise, which is important for healthy weight maintenance in people with diabetes)
- A significantly increased risk of low blood sugar (hypoglycemia)
- High blood sugar (hyperglycemia) resulting from a surge of stored glucose from the liver when low blood sugar levels result from fasting
It’s important to note that more research is needed to definitively back up the claims of side effects from intermittent fasting and to confirm the severity of such untoward reactions.
Because of the likeliness of side effects (such as hyperglycemia) from fasting when a person has diabetes, it’s important to consult with your healthcare provider before deciding to start any type of fasting diet.
There are several intermittent fasting diets that have had some preliminary research as to the effectiveness and safety of the diet for people with diabetes, including:
Thee 5:2 intermittent fasting (IF) diet (commonly referred to as the 5:2 diet) is one type of popular fasting diets, introduced in Dr. Jason Fung’s best-selling book “The Obesity Code” in 2016. The 5:2 diet involves five days of eating the recommended daily caloric intake and two non-consecutive days of eating a reduced-calorie diet. On fasting days, food is not eliminated altogether, rather, the number of calories is reduced.
If you have diabetes and want to try the 5:2 diet, speak to your healthcare provider or diabetic team and get a recommendation for a daily caloric intake guideline for fasting and non-fasting days.
Studies on the 5:2 Diet
Studies have shown that the 5:2 diet may help reduce insulin resistance and promote weight loss in people with type 2 diabetes or prediabetes.
The first long-term study of the 5:2 diet, published in 2018, by the Journal of the American Medical Association (JAMA), discovered that intermittent fasting could be effective for those with diabetes who have trouble sticking to a long-term, daily diet regime. The study observed 137 people with type 2 diabetes; half of the study participants followed the 5:2 diet and the other half adhered to a daily calorie-restricted diet (comprised of 1200 to 1500 calories per day). The group that fasted for two non-consecutive days per week—consumed 500 to 600 calories on the fasting days and ate normally on the other five days of the week.
The study concluded that those who followed the 5:2 diet were just as likely to control their blood sugar levels as those who followed the ongoing restricted-calorie diet. “It [the 5:2 diet] may be superior to continuous energy restriction for weight reduction,” wrote the study authors.
Safety of the 5:2 Diet for People With Diabetes
While some experts claim that the safety of the 5:2 diet for people with diabetes has not yet been fully established, a long-term study published in 2018 reports that “fasting is safe for those with diet-controlled type 2 diabetes.”
The study authors conclude that those who take insulin or oral (by mouth) medications to reduce blood glucose levels (oral hypoglycemics) such as glyburide or metformin, require very close monitoring and possibly adjustments to medication doses, accordingly. This is because fasting is likely to cause hypoglycemia in those taking oral hypoglycemics or insulin.
Note, although this study result was very positive regarding the safety of fasting for those with diabetes, It’s important to consult with your healthcare provider before fasting, or starting any other type of diet.
Another type of intermittent fasting diet that has been studied in people with diabetes is called the “early time-restricted feeding (eTRF)” diet. Following this fasting meal plan means that a person will fit all their meals into a specific period of time each day.
The eTRF diet plan may be an 8-hour, 10-hour, or even a 6-hour plan. On the 8-hour plan, if a person begins 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 a person eats the first meal of the day at 7:00 a.m. and the last meal or snack would be planned for no later than 7:00 p.m.
How the eRFD Diet Works
The eTRF diet is thought to align with a person’s circadian rhythm in metabolism, thus, improving weight loss. Circadian rhythm refers to the body’s biological clock that controls many mechanisms, including cellular metabolism.
Changing the eating pattern to a period earlier in the day—thereby extending the overnight fast—was found to greatly benefit metabolism, but why? According to a study published in the New England Journal of Medicine, fasting triggers a few important cellular functions, such as lowering blood sugar and improving metabolism.
Benefits of the eTRF
Benefits thought to be derived from the eTRF diet include:
- Decreasing appetite
- Facilitating weight loss
- Increasing fat loss via oxidation (burning of fat)
- Lowering blood pressure
Study on the eTRF Diet for Diabetes
In a 2018 study, the 8-hour early time-restricted feeding diet was compared with the 12-hour diet. The study discovered that the 8-hour group had dramatically lower insulin levels; both groups (the 8- and 12-hour group) maintained their weight (neither losing or gaining weight) and achieved significantly lower insulin levels, as well as lower blood pressure.
According to Diabetes UK, there are some general tips that are important to follow if you have diabetes and you plan to start an intermittent fasting diet. These include:
- Consult with your healthcare provider or diabetes team regarding whether intermittent fasting is recommended for you; if so, follow the team’s advice on medications for diabetes (regarding time or dosage changes) to ensure blood glucose level control.
- Maintain a balanced diet during the fasting periods as well as the non-fasting periods, including foods from all of the food groups.
Do not eat excessively during the non-calorie restricted periods.
- Include foods that are more slowly absorbed, such as those considered lower on the glycemic index scale, just before you fast (these foods are typically high in fiber and are digested slowly).
- Be sure to eat foods that fill you up and maintain your blood sugar during the fast, such as fruits, vegetables, and fresh salads.
- When you break the fast (for example, in the morning after a 12-hour fasting period) limit the amount of fatty or sugary foods and try grilling or baking foods instead of frying.
- Drink plenty of fluids during the fast to avoid dehydration (avoid sugary drinks).
- Test your blood glucose levels often to check for either hypoglycemia or hyperglycemia.
- If you experience symptoms of hypoglycemia, it’s vital to break the fast immediately, and use your normal course of action (such as taking glucose tablets, followed by a snack). Consult with your healthcare provider before continuing the fast.
- Those with type 1 diabetes should observe for signs of hyperglycemia as a result of fasting (including extreme thirst and frequent urination as well as severe fatigue. Contact your healthcare provider right away if you experience these symptoms and blood sugar levels remain high.
The safety of fasting for those with type 1 diabetes has not been fully established. You should never fast if you have type 1 diabetes without first consulting with your healthcare provider.
According to Harvard Health, there are some general recommendations on how to utilize recent medical science breakthroughs about intermittent fasting for those with type 2 diabetes (or prediabetes), these include:
- Avoiding snacking to allow the body to burn fat between meals.
- Avoiding refined (white) sugar and grains (such as white flour), opt for whole grains instead.
- Eating fruits, vegetables, beans, lentils, and lean proteins as well as good fats (from unsaturated, non-trans-fat sources) and whole grains (such as quinoa, oats, and brown rice).
- Avoid eating any type of snacks or meal before bedtime.
- Consider a simple form of intermittent fasting (after consulting with your healthcare provider) limiting food intake to between the hours of 7 a.m. and 3 p.m. or 10:00 a.m. to 6:00 p.m.