Intermittent Fasting: Not So Fast

Keeping up with the latest “diets” has never been easy. There’s always a new crop of them that pop up, and many become all the rage for a while, garnering avid followers and fierce proponents. And when it comes to delivering on results, such as weight loss, most diets work. Whether you can stick with a diet for a given length of time is another story, however.

Advertisement

Diets that are hot right now include the ketogenic, or keto, diet, low carb, the carnivore diet and intermittent fasting. The very word “fasting” is probably less than appealing, as it pretty much means you don’t eat or drink anything (except perhaps water) for a specified amount of time. Most health-care professionals don’t routinely recommend this for health purposes. But intermittent fasting is different. Is it safe to do if you have diabetes? And is it something you should try?

What is intermittent fasting, anyway?

Intermittent fasting has has grown in popularity over the past few years, in part, due to two books: The Fast Diet by Dr. Michael Mosley and Mimi Spencer, and The Overnight Diet by Caroline Apovian, MD. Intermittent fasting essentially means that you skip a meal or severely restrict calories on certain days of the week with the intention of losing weight, controlling blood glucose, and/or decreasing heart disease risk. But on the other days of the week, you can pretty much eat what you want (within reason, of course). For many people, this concept sounds appealing. Limiting calories for a couple days a week doesn’t sound that bad if you can eat what you want the rest of the time.

On The Fast Diet, also called the The 5:2 Diet has you eat between 500 and 600 calories (women get 500 calories, men get 600 calories) for two days out of the week, spread over two meals of about 250 to 300 calories. These fast days should not be right in a row, and your food choices ideally should be more plant-based and emphasize protein. The premise is that after several hours of fasting, the body burns up its carbohydrate stores and shifts to burning fat for fuel. Many claim that intermittent fasting also helps to blunt appetite.

The Overnight Diet emphasizes getting enough sleep; a lack of sleep can disrupt metabolism, making it hard to lose weight. Sufficient sleep, according to the author, will reduce hunger pangs. The diet part of this involves drinking homemade smoothies once a week, and eating a low-calorie, high-protein diet the remaining six days of the week.

Does intermittent fasting work?

Is intermittent fasting just another passing fad? Maybe, but there actually is some credible science behind fasting. Restricting calories in the diets of animals appears to increase their lifespan, for example. A team of researchers in the UK looked at the various approaches to intermittent fasting, with a focus on how they might help (or hinder) those with Type 2 diabetes and obesity. They found that intermittent fasting is as effective as or even more effective than simply cutting calories to lose weight.

They also found that intermittent fasting has other health benefits, including reducing inflammation, lowering blood pressure, lowering heart rate, lowering cholesterol and reducing insulin resistance. This unique approach may even help prevent the development of Type 2 diabetes. Followers of the diet also believe that intermittent fasting can prolong your life and prevent Alzheimer disease.

A recent study out of New Zealand involved 41 participants with Type 2 diabetes who were assigned to the 5:2 fasting diet. They could eat what they wanted for five days a week, and then “fasted” for the next two days (“fasting” was actually a 600-calorie diet for men, and a 500-calorie diet for women). Half of the group were instructed to fast for two days in a row during the week, while the other half fasted on non-consecutive days.

The results? After 12 weeks, A1C levels dropped in both groups from 8.4 percent to 7.8 percent in the consecutive group and from 8.2 percent to 7.5 percent in the non-consecutive group. Both groups lost about the same amount of weight (on average, 8 pounds in the consecutive group, 7 pounds in the non-consecutive group).

You might be thinking, “That’s great — they lost weight!” Yes, they did, but the amount of weight lost over 12 weeks, while commendable, is less than what most lower-calorie eating plans recommend (a loss of between 1 and 2 pounds per week). In addition, in this study, the risk of hypoglycemia (low blood glucose) increased during the fasting days, and that’s not surprising. What’s interesting, however, is despite the hypoglycemia, the participants still managed to lose weight and lower their A1C. (Frequent hypoglycemia may lead to weight gain in some people due to having to treat the lows with carbohydrate).

In another study, published in BMJ Case Reports, three men with Type 2 diabetes treated with insulin between the ages of 40 and 67 tried intermittent fasting for 10 months. Two of the men fasted every other day for 24 hours, while the third man fasted for three days a week. “Fasting” in this study consisted of a low-calorie meal at night and non-caloric beverages. All of the men were able to stop taking insulin between 5 and 18 days into the regimen. Two of the men were able to discontinue their other diabetes medicines altogether. In addition, they all lost weight (between 10 and 18 percent), reduced their weight circumference and lowered their A1C. Hypoglycemia wasn’t a concern.

Is intermittent fasting for you?

Intermittent fasting may seem intriguing, if not downright appealing. But before you jump on the fasting bandwagon, realize that research this area is still relatively new, at least with humans. It’s true that the few studies thus far look promising — not just for A1C and weight reduction, but for lowering blood pressure and cholesterol, as well. But there aren’t long-term studies to indicate if this dietary approach is safe, effective or sustainable.

A review of 40 studies showed that a typical weight loss over a 10-week period ranged from 7 to 11 pounds. That’s pretty good, but not earth-shattering. The review also showed that intermittent fasting isn’t necessarily any easier to follow than other dietary approaches. In a randomized controlled trial of 100 obese individuals who did either alternate-day fasting or a calorie-restricted diet with three meals per day, there were no significant differences between the two groups in the amount of weight lost or regained, fasting glucose, fasting insulin, heart rate, blood pressure and total cholesterol (although LDL was higher in the alternate fasting group).

The appeal of being able to lose weight and decrease (and maybe even discontinue) some or all of your diabetes medication is certainly strong. But what DO you eat on an intermittent fasting plan? A sample 500-calorie menu from The Fasting Diet is steel-cut oatmeal with 1/2 cup of blueberries for breakfast, and then chicken stir-fry made with 5 ounces of chicken and some vegetables, along with a tangerine for dinner. That’s it. Would that hold you?

Could intermittent fasting be harmful?

Well, that depends. If you take insulin or sulfonylurea drugs to control your blood glucose, intermittent fasting can considerably raise the risk of low blood glucose unless you make appropriate adjustments. Intermittent fasting is not suitable for:

• pregnant women or women who are breastfeeding
• people under the age of 20
• people who are underweight
• people who have an eating disorder

It may also not be good for people who take certain types of medicines, such as beta-blockers.

Side effects of this diet include:

• extreme hunger
• irritability
• weakness
• shakiness
• fatigue

There’s also some concern that intermittent fasting may trigger binge eating. Another question to ask yourself: Can you really stick with this way of eating? It may sound simple to just eat 500 calories for two days a week, but 500 calories isn’t all that much. On those days, you’re likely to feel tired, grumpy, anxious and irritable. You also may not sleep well and your breath might not exactly smell like a bed of roses. You may have difficulty concentrating and performing at work or school.

If you’d like to give intermittent fasting a try, talk it over first with your health-care provider and decide together if it’s something that could work for you. If you’re determined to give it a go, at least inform your provider of your intent and discuss a plan for possibly decreasing your diabetes medication doses to prevent or limit hypoglycemia. Consider meeting with a registered dietitian who supports your goals to work out a plan (not all intermittent fasting diets follow the 5:2 approach). And if you have tried this, feel free to share your experience!

Want to learn more about diabetes and fasting? Read “Can Fasting Help Diabetes?” and “Fasting During Ramadan.”

Learn more about the health and medical experts who who provide you with the cutting-edge resources, tools, news, and more on Diabetes Self-Management.
About Our Experts >>