Ep. 112: All About Intermittent Fasting with Leslie Beck & Dr. Krista Varady
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Intermittent fasting is an increasingly popular diet method intended to trigger weight loss. It’s also said to provide other health benefits. But does it actually work? And which form is appropriate for which people? Dr. Krista Varady is a University of Illinois, Chicago professor of nutrition and a globally recognized expert in intermittent fasting. Here she discusses her recommendations with Leslie Beck, the Globe and Mail nutrition columnist and Medcan’s Director of Food and Nutrition.
LINKS
Dr. Krista Varady was the lead author on a recently published review of the science on the three most-researched forms of intermittent fasting: Clinical application of intermittent fasting for weight loss: progress and future directions in Nature Reviews Endocrinology. Plus, here’s a University of Illinois, Chicago news release on the review: Research team provides guidelines, recommendations for intermittent fasting.
Dr. Krista Varady is on Instagram @drkristavarady. Her academic bio page is here.
Leslie Beck wrote about intermittent fasting and Dr. Krista Varady’s Nature Reviews Endocrinology paper in the Globe and Mail. Here’s her article. Plus, back in 2019, Leslie wrote a comprehensive guide about the topic. And Leslie’s interview with another fasting researcher, Dr. Ethan Weiss, is here.
Dr. Krista Varady’s book is The Every-Other-Day Diet: The Diet That Lets You Eat All You Want (Half the Time) and Keep the Weight Off.
The New York Times’ Well blog features Dr. Krista Varady in its coverage of intermittent fasting here and here.
Still curious to learn more after listening to this episode of Eat Move Think? Here’s another podcast featuring Dr. Krista Varady.
Interested in working with Leslie Beck’s team of registered dietitians to incorporate intermittent fasting into your wellness routine? Make an appointment with Medcan Nutrition.
INSIGHTS
Intermittent fasting is simpler, more affordable and more straightforward than other diets. No calorie counting, no food tracking. “If we look back at all the other fad diets that happened over the past 20 or 30 years, with low fat diets, or low carbohydrate diets, there was always this emphasis on not only tracking calories, but also tracking carb intake. And it was just so complicated for people,” says Dr. Varady. “So this one is a totally different approach, where instead of focusing on those macronutrients, like carbs and fat, we're really just focusing on meal timing… So it's really accessible. I think people love that about it. They love the fact that there's this diet that allows you to eat freely during certain periods of the day, or on certain days of the week.” [4:09]
Leslie Beck asked Dr. Varady to describe three most researched forms of intermittent fasting. “Intermittent fasting is really an umbrella term for three different kinds of diets,” says Dr. Varady. “The first one is alternate-day fasting. And that's when people have a fast day, where you consume either just water or about 5-600 calories at a dinner, usually, or maybe a lunch. And then that's alternated with a feast day, where people can just truly eat whatever they want. We ask people to focus on a healthy diet, but you don't have to track anything, or worry about calories, or carbs or anything. So alternate-day fasting, really just kind of flip flops between feasting and fasting… The 5:2 diet is the second type. And that is a spin off of alternate-day fasting, where people have two of those fast days per week, and you can put those fast days wherever you want… And then the most popular one… is time-restricted eating. That's really simple—you basically just eat within a certain window of time each day, and it's usually about eight hours or so.” [5:45]
Leslie Beck asks, Does it work to help people lose weight? “I'd say it definitely works,” says Dr. Varady. “So I've been studying intermittent fasting for the past 15 years or so… What we found, just reviewing all the research articles in the field, is that it results in about 4 to 8% weight loss in about three months or so. So for a lot of people that translates to anywhere from 10 to 20 pounds, and about three months, People are able to maintain weight loss. There's a few longer-term studies showing that if you continue a modified form of these diets… you can maintain the weight loss.” So why do people lose weight? Beck asks. “I’m really glad you asked that,” says Dr. Varady. “Our lab’s probably run the most studies of intermittent fasting, [and] I'd say with certainty, it's just because people are eating less food.” [7:54]
“Your research summary… also looked at how effective intermittent fasting was for lowering blood cholesterol and blood pressure,” Leslie asked. “What does the evidence say?” Dr. Varady responds, “Yeah, so not only does it produce weight loss, but it can definitely help with lowering cholesterol levels and blood pressure as well. The different types of protocols have been shown to lower LDL cholesterol, so that bad cholesterol, by anywhere from about 10 to 25%. And then blood pressure, we also see pretty consistent reductions, and it's mainly systolic blood pressure… And that usually goes down anywhere from 10 to 15% with most of these diets.” [17:06]
“Some people, though, get cranky and irritable, and they are less able to concentrate when they go without food too long,” says Leslie. “Does your research show that this is the case for intermittent fasters?” “So no,” says Dr. Varady. “We actually find that people have a boost of energy on fast days. Well, I do have to point out the first 10 days are a little rough, I'm not gonna lie. But in all of our studies, with time-restricted feeding and alternate-day fasting, there is that adjustment period. Our bodies do take a few days to kind of adapt to a new pattern of eating. But once people are past that, they actually feel great. And a lot of people have said that they actually have a boost of energy during the fasting period. And I think I mentioned in the article that basically, this might be linked to some type of evolutionary thing where if we don't have food, our bodies will give us energy to go out into our environment and find food potentially. So maybe that's what it's from. But you don't have to worry, you're not going to feel terrible while you're fasting the whole time. Just, you know, [the] first couple days and then after that people feel great.” [21:59]
“So who should not try intermittent fasting?” Leslie asks. “There's several groups that should not do intermittent fasting,” says Dr. Varady. “Children under 12, for instance… those children are growing, they should not be probably calorie restricting or intermittent fasting. Women who are pregnant or lactating, there's no safety data around that. So it's probably not recommended for them at this point. People with a history of eating disorders, particularly binge-eating disorders, those individuals don't tend to do well with alternate-day fasting. They tend to binge on the feast days. Whereas the average person just doesn't binge on the feast days… People that are underweight should not do it. And then there's also really not that many studies in people over 70 years old. When somebody hits 70, their lean mass starts to go down quite a bit. So I probably wouldn't recommend it for them just because we don't want to exacerbate sarcopenia, or muscle mass loss.” [27:01]
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