December 2014 Issue

Intermittent Fasting: The Key to Long-Term Weight Loss?
By Beth W. Orenstein
Today's Dietitian
Vol. 26 No. 12 P. 40

Could feast or famine be the path to sustainable weight loss and good health? The answer depends on whom you ask. The diet known as intermittent fasting, where one eats normally some days and little to nothing other days, lately has gained much attention around the world. Proponents of intermittent fasting believe it's a good way to not only shed pounds quickly but also to reduce risk factors for diabetes and heart disease. Others see intermittent fasting as a poor choice for dieting and harmful to one's health. Some worry that fasting robs the body of important nutrients and could send it into starvation mode, making sustained weight loss more difficult.

History of Fasting
Men and women of faith have fasted for religious reasons for centuries. During Ramadan, the ninth month of the Islamic lunar calendar, observant Muslims eat only before dawn or after sunset for 30 days. On Yom Kippur, the Day of Atonement, which usually falls in September or October, Jews refrain from eating and drinking, even water, from before sunset to sundown the following day. Fasts accompanied by acts of charity are a large part of the Hindu religion. Many Hindus observe a fast in the name of God at least one day per week. And many Christians fast and pray for 40 days during the Lenten season or periodically throughout the year when there's a need to reinforce spiritual discipline, receive direction from God for their lives, or experience divine intervention during tough times.

Fasts also have been used to express social and political views throughout history. Mahatma Gandhi engaged in several well-publicized fasts to protest the British rule of India. The black comedian and civil rights activist Dick Gregory also gained attention for his many hunger fasts. Throughout history, prisoners have been known to go on hunger strikes.

Some people have tried fasting to lose weight before a big event such as a wedding or class reunion. But intermittent fasting took off as a weight-loss craze at the very end of 2012 when British journalists Michael Mosley and Mimi Spencer published their book the FastDiet. In it, they advocate 5:2 intermittent fasting: Two days per week you limit yourself to less than 500 kcal if you're female, and 600 kcal if you're male. The remaining five days you eat as you normally would. The authors contend the diet won't only allow you to drop pounds quickly but also lower your blood pressure and cholesterol and improve your insulin sensitivity. Mosley, who was trained as a doctor at the Royal Free Hospital in London, wrote the book after using intermittent fasting to improve his health and lose more than 20 lbs.

It didn't take long for the buzz about 5:2 to make its way across the ocean, says Joy Dubost, PhD, RD, CSSD, a dietitian in the Washington, D.C., area and a spokeswoman for the Academy of Nutrition and Dietetics. "It's been a trend in the US almost two years now," she says. While not a new idea, Dubost says, "None of the other fasting diets has been as popular as this." Fasting diets are similar in a way to quick-weight-loss cleansing diets, which have been making headlines, too, Dubost says. Some cleansing diets require eliminating solid food for one or two weeks and consuming only liquids. They're similar to fasting diets in that people consume less than 700 kcal per day when on them.

Heather Mangieri, MS, RD, CSSD, of Nutrition CheckUp, a nutrition consulting practice in Pittsburgh, believes that interest in intermittent fasting already has begun to fade. "I heard less about it this past year," she says. However, Mangieri wouldn't be surprised if intermittent fasting were to become popular again at any time. "It comes and goes," she says, and has no doubt "it will be back again."

Fasting Diets Differ
It's important for dietitians to keep in mind that not all fasting diets are the same. The fasting diet can be two days on and five days off as The FastDiet advocates. Or, it could involve 24-hour fasts one or two times per week, or randomly skipping meals, says John Berardi, PhD, CSCS, founder of Precision Nutrition, a fitness and nutrition coaching business based in Toronto, Canada, and author of the e-book Experiments With Intermittent Fasting. Krista Varady, PhD, an associate professor of kinesiology and nutrition at the University of Illinois at Chicago, has studied fasting diets during which participants fast every other day. She calls it alternate-day fasting, and by fasting she means eating very little (eg, consuming 25% of one's normal caloric need). That's about 400 to 500 kcal for women and 500 to 600 kcal for men. Some people spread their 500 kcal over three tiny meals, but according to Varady consuming the calories in one meal between noon and 2 PM is best for most people because it breaks up the day.

Varady's research shows that fasting diets can be beneficial. She has published about 20 different studies on alternate-day fasting and is completing a one-year study funded by the National Institutes of Health that's evaluating patients on alternate-day fasting for the first six months and on a higher-calorie diet for the rest of the year. One of her recent studies published in the November 2013 issue of Nutrition Journal randomly divided into two groups 32 subjects who were at a normal weight or overweight. One group practiced alternate-day fasting for 12 weeks, while the control group ate normally. Varady found that those in the alternate-day fasting group lost approximately 1 lb per week and experienced cardioprotective effects at the end of treatment. The patients in the alternate-day fasting group saw their triglyceride concentrations decrease 20% and their LDL particle size increase relative to the control group. Patients whose LDL particles are small and dense have a greater risk of coronary heart disease. "We believe the weight loss is responsible for the lipid lowering," she says.

In her research, Varady also found that alternate-day fasting seemed to help lower diabetes risk. A review of 12 animal and three human trials she published in the July 2007 issue of the American Journal of Clinical Nutrition found a lower diabetes incidence and reduced fasting blood glucose and insulin concentrations in those following alternate-day fasting diets. But Varady says larger sample sizes are needed before "solid conclusions can be reached."

How and Why Fasting Works
Fasting works, proponents believe, because the dieter eats less in one week than they normally would; any time a person consumes fewer calories than he or she burns, that person should lose weight. Varady says that for some people alternate-day fasting can be easier than reducing the number of calories they eat each day. In her studies, researchers help participants by showing them how much food 500 kcal looks like and in some cases supply meals. Moreover, Varady says that what helps get dieters through fast days is knowing that on feed days they will feel normal again. With reduced-calorie diets, they're hungry all the time.

Mangieri says one of the reasons fad diets such as intermittent fasting get so much attention is because they offer new hope for people caught in the yo-yo diet cycle. People like intermittent fasting because they just want to be told what to do. "In the short term they're relieved of the stress of figuring out what to eat," she says.

The key to intermittent fasting is not to overeat on "feed" days. When Varady started her research, she was skeptical about whether fasting would work. She assumed that people would overeat on days they could eat because they were famished from their fast. To her surprise, she found that her study subjects didn't binge on feed days, and that's how they were able to successfully lose weight. "My research shows that on feed days, people are only eating about 10% more than they usually eat so they're not making up for all the calories they didn't have on fast days. That's why they're losing weight," she says.

Varady also found that fasting didn't lower participants' resting metabolic rate as some believed it would, although she hasn't yet published this finding. With most diets, she says 75% of what people lose is fat and 25% is muscle. With alternate-day fasting, it's 90% fat and 10% muscle, according to a study in the January 2013 issue of Metabolism and a study in the November 2009 issue of the American Journal of Clinical Nutrition. That's why it doesn't change your resting metabolic rate, which is key to weight loss, Varady says.

Impact of Physical Activity
Exercise always has been seen as an important complement to successful weight loss. The idea is the more calories you burn, the more weight you lose. Some researchers were concerned that fasters wouldn't be able to exercise, especially on fast days. But Varady found that wasn't the case with her subjects as long as they exercised in the morning before they had their meal. "You get a hunger surge a half-hour after exercise," she says, and if people exercise in the afternoon and aren't supposed to eat until the next afternoon, "then it's harder for them to stick to the fast part of the diet." Berardi was cycling and running several hours a week even on days he fasted. He found that he had more success if he performed intense exercise on the days he ate, he says.

Research on athletes who fast during Ramadan has shown significantly reduced performances and increased perception of fatigue during the fasting period, according to one study published in 2011 in the International Journal of Sports Studies. In this study, researchers tested the athletic endurance of 15 male runners aged 20 to 25 one week before the beginning of Ramadan and during the middle of Ramadan. The results showed that Ramadan fasting had a small significant impact on endurance running performance. More research is needed to determine if Ramadan-style fasting has an impact on more complex sporting events.

However, a study published in the June 2010 issue of the British Journal of Sports Medicine found that Ramadan-style fasting had a small negative impact on athletic performances. And a study published in the June 2012 issue of the Journal of Sports Science found that Muslim athletes who maintain their total energy and macronutrient intake during Ramadan don't suffer any substantial drop in performance.

What Research Shows
Despite the evidence that intermittent fasting can cause weight loss and improve risk factors for heart disease, many dietitians remain skeptical and wouldn't recommend the dietary pattern as a weight-loss tool or method to improve heart health in most people. "There are better diets that we have long-term evidence on," Dubost says. "There are just too many unknowns, especially long term, with this." It isn't a good approach for women who are pregnant, or anyone who has diabetes or who has other health conditions, especially those that require medications, she says, adding that she can't fathom how otherwise healthy people can remain active and not eat. Fasting can make people dizzy, lightheaded, tired, and nauseated. "Your workouts may suffer as a result," she adds, noting that it's better for people to make healthful, well-balanced dietary choices each day and get the nutrients and exercise they need rather than fast on and off.

Moreover, one study found that intermittent fasting could harm heart health. A study published in the October 2010 issue of The Journal of Cardiac Failure found that rats on intermittent fasts for six months developed stiffened heart tissue. As a result, their hearts didn't pump blood as effectively. Conversely, other animal studies suggest that intermittent fasting may have some heart health benefits similar to calorie restriction such as improving heart rate and lowering blood pressure and cholesterol. In the March/April 2013 issue of The British Journal of Diabetes & Vascular Disease, researchers found improvements in blood pressure and heart rate in animals on intermittent fasts. The researchers also found that severely restricting the animals' calories lowered circulating cholesterol and triglycerides and increased resistance to injury caused by reduced blood supply to the heart. The researchers' theory is that fasting can protect the heart by raising levels of adiponectin, a protein that plays a role in metabolizing carbohydrates and fat.

Research on the impact of intermittent fasting on people with diabetes has suggested that it can lead to hypoglycemia. A retrospective study of more than 12,000 people with type 1 and type 2 diabetes, published in the October 2004 issue of Diabetes Care, found that those who fasted during Ramadan experienced frequent bouts of severe hypoglycemia especially if they didn't adjust their medication or exercise patterns. According to a study published in the February 2013 issue of the Iranian Journal of Reproductive Medicine that evaluated women who fasted during Ramadan for more than 15 days, researchers found that the women had more abnormal menstrual cycles than those who fasted fewer days.

Dubost says intermittent fasting isn't a healthful way to lose weight. Once someone has lost weight with intermittent fasting, she says they can gain back the weight more quickly once they start eating normally because during fasting the person's body can go into starvation mode to conserve energy. "Your body is forced to dip into its energy stores and that can mess with your metabolism," she says. And if someone resets their metabolism during fasting, they can gain weight even if they eat very little, she adds. However, whether fasting definitely can slow metabolism is questionable. In a study published in the March 2011 issue of the Journal of the International Society of Sports Nutrition, researchers concluded that there's no universal consensus regarding the effects of meal frequency on metabolism markers.

Counseling Clients
If clients ask about intermittent fasting, Mangieri suggests dietitians "Find out why your client is interested in following a diet that promotes fasting and educate them on what we know about it," she says. "It's ultimately their choice whether to take our advice."

Mangieri says individuals who wish to try intermittent fasting should ask their RD whether they should take vitamin and mineral supplements and what foods they should eat on nonfasting days. "It's the registered dietitian's job to help clients understand that whether restricting food or not, it's important to include a variety of healthful foods, including lean proteins, fruits, vegetables, a few servings of whole grains, low-fat dairy, and some healthful fats in their diets," she says.

If a client is adamant about following any particular eating plan to lose weight or improve their health, Mangieri says she'd go along with that plan but teach the client how to tweak it to make it nutritionally sound. Dietitians are trained to individualize plans. "We teach clients how to meal plan using foods that they like, that will meet their nutritional needs, while helping them figure out how to make it happen with their work, family, and social obligations."

Dubost says she wouldn't advise clients to try intermittent fasting, "because I don't think there's enough evidence to support its recommendation." If her clients insisted, she would at least recommend that on days they eat, they make sure they choose nutrient-dense foods and get what they need for their health. According to Dubost, people must understand, "it's not what you do on any given day. It's what you do over time that counts."

Varady believes intermittent fasting isn't for everyone. "It works best for people who aren't snackers," she says. "If you need to eat something small every two hours, alternate-day fasting isn't for you." But if you're too busy to eat or like the idea of up and down eating, it can work. Varady says when she first started her research many colleagues thought potential study participants wouldn't volunteer for alternate-day fasting. "But it's nice," she says, "that it's out there as another option for people to lose weight."

— Beth W. Orenstein is a freelance writer living in Northampton, Pennsylvania.