You’re on the keto diet and loving the results you see. But you can’t help but wonder if you can give your weight loss even more of a boost by trying another intriguing diet regimen in tandem—intermittent fasting (IF). IF is basically a weight loss plan in which you avoid eating for periods of time—on alternate days, for instance, or more popularly, through time-restricted eating, where you schedule all your your meals into a daily time window—say, 7 a.m. to 3 p.m., or carefully spread between 7 a.m. and 7 p.m. (It’s also sometimes known as the OMAD diet, or “one meal a day.”) The question is, the combination of keto and intermittent fasting safe?
“The most important thing is to make sure you’re meeting your nutritional needs,” says Ginger Hultin, a Seattle-based registered dietitian, spokesperson for the Academy of Nutrition and Dietetics and owner of ChampagneNutrition. “That means working with a medical team.” If your doctor does sign off, how exactly does an IF-keto regimen work—and what are its true benefits? Let’s take a closer look.
How the keto diet and intermittent fasting work individually
If you’re not familiar with the principles of the keto diet, here’s what you need to know. “The ketogenic diet is very low carb—carbs are limited to 40-60 grams per day, and more than 80% of your calories come from fat,” Hultin explains. “Keto is a moderate protein diet—it’s designed to force the body into a fat-burning state called ‘ketosis’. Ketosis uses an energy source called ketone bodies to fuel the brain. So your body is forced to break down fat rather than using glucose, or blood sugar, for fuel. When the glucose in your body is depleted, ketone bodies are created. Then, those ketone bodies cross your blood/brain barrier as energy for your brain and central nervous system.”
Intermittent fasting is built around a more simple concept: good old-fashioned calorie restriction. “Intermittent fasting can be done in a variety of ways,” Hultin says. “The overall foundation, though, is based on a period of extended time where you go without eating—a fast. Many people on IF do this for 12-16 hours overnight, and eat their first meal at lunch or mid-morning.” Not only are calories cut back this way, but “IF proponents believe that this schedule helps with digestion, too.” Hultin adds. And it seems to be highly effective: a recent overview of research on intermittent fasting found that as a whole, if you’re in good physical and emotional health, this kind of plan on its own won’t hurt you. Indeed, almost any intermittent fasting plan is going to result in some level of weigh loss, too, according to the overview’s authors.
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What are the benefits of intermittent fasting and keto together?
If you work IF into your keto plan, one big plus you may notice is that you reach ketosis faster. Why? Fasting causes your body to move its fuel reserve away from carbs and onto fats, which is, of course, the same way keto causes you to lose weight. Plus, your body burns fat for energy when you fast—another keto-friendly concept. It usually takes a couple of days for your body to start kicking into weight loss mode on keto, so conceivably, intermittent fasting could give you a leg up on dropping some pounds out of the gate.
Is it safe to combine keto and intermittent fasting?
“It really depends on the person,” says Hultin. “For example, if you take certain medications, fasting may not be safe. If you have blood sugar problems or are on blood sugar lowering medications, either one of these diets could be extremely dangerous or even deadly.”
Obviously, if you’re pregnant, any form of weight loss diet will not be right for you. Likewise, if you have other chronic conditions, you need to abstain, period, if your doctor tells you to.
It’s also key to talk to your doctor about how the specifics of keto could interact with IF—if you currently take the cheat day, for instance. A study from the University of British Columbia found that the simple act of taking advantage of a cheat day while on keto could mean you consume as little as 75 grams of glucose and potentially damage your blood vessels. Sugar and high-fat, low-carb could make for a dangerous mix, first and foremost. Toss in further calorie restriction, and things could get a little complicated in terms of the specifics of your long-term health. Your best bet: have a physical to get a baseline profile of your health status before putting IF and keto together.
How do you combine intermittent fasting and keto?
Here are some tips on how to get the most out of your IF-keto regimen.
Know your overall objective.
“Focus on meeting your caloric needs to stay healthy,” stresses Hultin. “You need to make sure you’re getting the right amount of protein spaced throughout the period of time that you are eating on IF, because there are limits to how much protein the body can absorb and utilize at a given time. You also have to ensure that your vitamins and minerals are being met as well. You’ll also need to consider how much fiber and fluids you need, and factor that in.”
A new study from Johns Hopkins suggests that intermittent fasting could be part of a healthy lifestyle, but that physicians advise patients to gradually increase the duration and frequency of the fasting periods over the course of several months, instead of “going cold turkey.”
Restrict the hours of the day when you eat to between 7 a.m. to 3 pm, or 10 a.m. to 6 p.m. It’s better to fast closer to bedtime.
Consult a dietitian.
Combining two plans like IF and keto is often most successful when you work with a pro. “People underestimate how critical having a dietitian on their team can be,” Hultin says. “We really know the ins and outs of keeping people safe, and meeting their needs can be a game changer. A registered dietitian or nutritionist can help you avoid eating disorder behavior, discuss your body image and relationship to food, and help you get on a balanced dietary pattern that you can stick with long term—but still helps you meet your health goals.”
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