Q: I thought intermittent fasting was a fad diet, but I heard a reputable speaker talk about it. What do you think? RJ, Greenville.
A: Once considered a fad, intermittent fasting is the target for serious research. The results of new studies do not paint a clear picture for us. Connie Zhong, a Brody medical student will tell you what we know about intermittent fasting as of today.
It could change. If you are on medications, however, talk with your doctor before you try this approach to weight management.
In recent years, various diets such as the ketogenic diet, vegan diet, paleo diet, and intermittent fasting have gained popularity in the news for their advertised results.
Intermittent fasting is when one stays away from eating or drinking for a certain amount of time or certain amount of food. One example is alternate-day fasting, when one fasts for one day, then the next eats whatever he or she wants. Research studies have shown mixed results but have documented a possible decrease in cholesterol and perhaps an average of a 2.5% reduction in weight in 22 days. Thus, someone who weighed 200 pounds would lose around 5 pounds in 3 weeks. However, extreme hunger and its negative effects on work and mood may make it difficult to stick to an alternate-day fasting regimen. A person might not be able to concentrate or have no energy on the day without food.
Another example is modified fasting, where one restricts how much he or she eats by 20-25% --or cutting out 400 – 500 calories if you eat 2000 calories a day-- on 2 days of the week. There are no limitations on eating the other 5 days. Several studies have shown weight loss, ranging from 3% to 8% (or 6 to 16 pounds for a 200 pound person) in 2 or 3 months. Cholesterol, fat, and insulin levels may go down in some but not all people who try this diet. Many overeat on days off or eat a high fat or sugar diet. If you do this type of fast, it is important to eat healthy foods and drinks on the 5 “off” days. Be mindful and eat vegetables at every meal and stay away from sugar sweetened drinks. Unlike alternate-day fasting, people who did modified fasting actually reported feeling more full and had generally improved mood.
The last example is time-restricted fasting, when one only eats at certain hours of the day---such as from 9 am-6 pm. Some studies have shown weight loss of 2- 4 % (or 4-8 pounds for a person weighing 200 pounds) in 8 weeks. Other studies report no change in weight, fat, or insulin levels.
The benefits of fasting may be due to a couple of different effects. The first is its effect on the circadian clock. Animals including people have an internal clock that is in charge of your sleep/wake cycle. Eating outside of the normal time frame --like late at night-- can disrupt the clock and affect the liver, fat, and muscle cells. Because your body is not as sensitive to sugar from meals at night, your glucose levels may increase more than they would during the day. Your risk of type 2 diabetes, heart disease, and cancer may be higher if you regularly eat late at night.
The second effect is on your gut microbiota. Your gut has a lot of bacteria and other tiny microorganisms that affect how you metabolize or break down your food. Eating within particular time frames during the day leads to more fluctuations in amount and type of bacteria during the day. Having increased variety of bacteria may help improve your body’s process of breaking down food and using the nutrients in what you ate.
Fasting may also affect how much food you eat, how much energy you spend, and quality of sleep. People who intermittently fast may not eat as much because they simply have less time to eat. Although there has been limited research in humans, studies in mice have shown that fasting may lead to increased physical activity. Finally, eating late at night has been shown to disrupt sleep – both decreasing the amount and quality of sleep. Poor sleep is linked to higher risks of diabetes, obesity, heart disease, and cancer. Thus, intermittent fasting can help you lose weight by simply decreasing the amount you eat and/or help you sleep better at night.
The bottom line is that there still needs to be more research before health care professionals can say if and who might benefit from this approach to weight management. Fasting is more likely to lead to improved health outcomes when combined with other lifestyle modifications such as exercising for at least 30 minutes a day, 5 days a week. People with certain health conditions such as diabetes should avoid intermittent fasting because of risks of extremely low blood sugar. People who take medications for high blood pressure or heart disease may also be at risk of adverse effects from having electrolyte abnormalities like low calcium, potassium, or magnesium. A visit with a Registered Dietitian Nutritionist can help you find the type of eating approach that would best meet your goals.