Double down on fat loss with these two metabolic firecrackers.
Nearly half of Americans report gaining weight since the start of the pandemic (1). Not surprising, given both stress and social isolation may be linked to weight gain (2, 3). If you’re looking to lose the pandemic pounds, some experts say you may want to combine keto and intermittent fasting.
Why is this a match made in fat-burning heaven? There is some evidence that keto and intermittent fasting both may help reduce inflammation (4, 5, 6). When done in tandem, these dietary practices may have an even more significant impact on weight loss.
Here’s how to start keto and intermittent fasting to reduce body fat fast.
Jonny Bowden, PhD, CNS, is the author of more than a dozen books and creator of Meta-Fasting.com.
Nephrologist Jason Fung, MD, is a world-leading expert on intermittent fasting and low-carb diets.
A ketogenic diet is a high-fat, moderate-protein, low-carb eating protocol that puts—and keeps—your body in a metabolic state called ketosis. In ketosis, your body switches from burning carbohydrates to fat as its main source of fuel.
Your body normally burns carbohydrates for energy. Those carbs are converted into glucose, a simple sugar that serves as a major fuel source for your organs, tissues, and metabolic functions through a complex process called glycolysis.
During glycolysis (7), glucose is split into smaller molecules (called pyruvate) for use as energy throughout the body. Our bodies can also create glucose from certain non-carbohydrate sources in a process called gluconeogenesis.
Glucose is the body’s first choice for fuel. But when you limit the amount of carbs that you eat, the body taps its stores of ketones—molecules created by the liver from fat—instead.
Think of your body like a hybrid car, which runs on electricity when the gas tank is empty. By limiting how many carbs you eat and switching to a high-fat diet, your body is forced to turn to fat as a fuel source instead.
When your daily carb intake is low enough—50 grams or less—you can usually get into ketosis in about 3 days.
Thanks to the metabolic switch from utilizing fat for energy instead of glucose, being in ketosis can be a fantastic weight-loss tool.
Studies have also suggested that the ketogenic diet may also have anti-inflammatory properties, may help prevent age- and neurodegenerative disease-related cognitive decline, and may help stabilize blood sugar in people with type 1 diabetes (4, 8, 9).
Scientists initially developed a ketogenic diet with the primary purpose of aiding in the management of seizures in children suffering from epilepsy. It was also used as an early form of type 1 diabetes management.
Intermittent fasting (IF) is exactly what it sounds like: splitting your 24-hour day into feeding and fasting windows. This is also commonly referred to as time-restricted eating (TRE), though some scholars suggest these practices differ slightly (10).
Many experts recommend starting with a ratio of a 12-hour fast to a 12-hour eating window and gradually working towards a 16:8 or 18:6 fast-to-eat split as you build up a tolerance to longer fasts, says the author of more than a dozen books and creator of Meta-Fasting.com, Jonny Bowden, PhD, CNS.
There are other fasting regimens, including:
The fasting regimen you choose may determine whether you enter ketosis from fasting alone. It generally takes anywhere between 18 to 48 hours without eating for a process called metabolic switching to kick in. Your body depletes its glycogen stores and starts to burn fat for energy — this is when the body enters ketosis.
IF is well known for its potential to accelerate weight loss but studies suggest that IF may also tout a ton of other health benefits, such as:
Now that you can see the similarities between keto and intermittent fasting, you’re probably wondering, “What happens when I combine these two metabolic powerhouses?”
“All the benefits of IF are increased if you also pay attention to what you eat during the eating window,” explains Bowden.
“Keto is known to accomplish many of the same goals [as IF] so adhering to a keto way of eating during your ‘eating window’ is a terrific way to accelerate your results,” Bowden says. Here’s what you might experience:
“Clinical experience tells us that doing keto and intermittent fasting at the same time tends to accelerate weight loss, especially if you are very weight-loss resistant,” says Bowden.
The average weight loss on a keto diet alone varies greatly from one person to the next.
“Some people will lose lots of weight, and others will lose none,” explains nephrologist Jason Fung, M.D., a world-leading expert on intermittent fasting and low-carb diets. “During fasting, the average weight loss is half a pound per day,” he adds.
According to Fung, when you combine keto and IF, the results are more predictable. “Weight loss occurs much faster with the combination of keto and IF.
It all depends upon how much fasting one is doing. If you did keto and fasted 16 hours a day, an average may be about one to two pounds per week, faster at the start and then slowing down.”
Insulin resistance, also known as impaired insulin sensitivity, is when cells in the liver, muscles, and fat tissue are unable to respond well to insulin and can’t access glucose from the blood for energy. The pancreas then over-compensates and makes more insulin, which can help temporarily, but over time the pancreas can’t keep up. Chronically high blood sugar eventually leads to health issues like diabetes, obesity, and associated cardiometabolic conditions such as high blood pressure and high cholesterol.
When you combine keto with intermittent fasting, you not only avoid food for long periods, which prevents blood sugar spikes, but you also consume a minimal amount of carbohydrates when you do eat.
The very low-carb nature of keto means glucose levels may remain steadier than on a typical standard or moderate-carb diet.
One small study found that people with type 1 diabetes who followed a very low carbohydrate diet had significantly improved blood sugar control (9).
Additionally, incorporating occasional fasting into your keto diet regimen may enhance the results for individuals aiming to control their blood sugar levels, whether to prevent or potentially reverse prediabetes or type 2 diabetes.
While acute inflammation is perfectly normal and healthy—think of bumping your elbow and experiencing swelling—the swelling is a protective inflammatory cell response that takes place in order to heal.
Chronic inflammation, on the other hand, is the kind you want to avoid because it means your body is in a constant state of defense, firing inflammatory cells even when there is no danger.
Chronic inflammation has been associated with conditions including rheumatoid arthritis, Alzheimer’s disease, cancer, and more.
Some studies suggest that the keto diet may help reduce inflammation (4). Being in ketosis means your liver is producing and releasing ketones which in some studies have been linked to a reduction in oxidative stress (11).
Studies also suggest that intermittent fasting may reduce inflammatory activity. According to a human and mouse-cell study led by researchers from Mount Sinai, intermittent fasting reduced the amount of pro-inflammatory cells called “monocytes” released into the bloodstream (12). During periods of fasting, these inflammatory cells went into sleep mode and were less inflammatory than monocytes found in those who were fed.
Research into the brain benefits of IF is beginning to show promising results for brain-related disorders and neurological diseases. Improved learning, memory, mood, and mental focus are some of the potential benefits that studies have begun to suggest from fasting (13).
Research suggests that intermittent fasting is a promising, innovative strategy that may help prevent and treat mental health disorders such as depression, as well as sleep disturbances, and cognitive impairment (14).
On the keto side, though research remains preliminary, there’s some evidence to suggest that a ketogenic diet may be beneficial to older adults with Alzheimer’s disease. Emerging research (15) suggests that being in a state of ketosis may have positive neurological effects on the aging brain.
The ketogenic diet may also help improve mood and well-being (16) by helping to ease depression and stabilizing mood, though this is supported by preliminary reports, and no clinical trials have been conducted.
Combining keto and intermittent fasting may help you lose weight, keep glucose levels stable, ward off conditions related to inflammation, and support healthy brain aging.
“You should not do keto if you have existing kidney disease,” says Bowden. Check with your health practitioner if you have any condition that might not benefit from either keto or IF, says Bowden.
Experts like Fung agree that you can get started with both a keto diet and intermittent fasting at the same time. But some research and easing into fasting should be your first steps.
Ahead of officially kicking off an IF plan, spend a couple of days cutting out snacks, delay breakfast time, eat an earlier dinner, and resist eating anything after dinner.
This phase is meant to condense your daily meals into a smaller window, eliminate snacking between meals and gradually extend your non-eating window in order to acclimate your body for longer fasting periods.
At the same time, sort out your keto meal plan. There is no shortage of cookbooks with menu plans to choose from. Determine which one suits your dietary style—some tend to be more meat-heavy than others.
It’s worth noting that diets high in animal-based foods have been linked to cardiovascular disease (17). Meat-heavy diets are also often void of fiber and antioxidant-rich plant foods, which play an important role in overall metabolic, cardiovascular, and gut health (18, 19). According to the American Heart Association, eating less meat and more plants decreases the risk of heart disease, stroke, obesity, high blood pressure, high cholesterol, type 2 diabetes, and many cancers (20).
For a more vegetable-forward plan, consider Ketotarian: The (Mostly) Plant-Based Plan to Burn Fat, Boost Your Energy, Crush Your Cravings and Calm Inflammation. Because IF naturally limits your daily caloric intake, there is no specific calorie guideline when you combine keto with intermittent fasting.
What matters more is the quality of the foods you eat in your feeding window. Eat nutrient-dense, whole foods, and aim to eat within your macro mix. According to functional medicine expert Will Cole, IFMCP, DNM, DC, and author of Ketotarian, the most common keto macronutrient breakdown is 75/20/5 (fat, protein, carbohydrates).
Now that you’ve determined your keto preferences and picked a meal plan, it’s time to start a fasting schedule.
Bowden recommends starting with a 12:12, where you fast for 12 hours and then have a 12-hour eating window. This means if you wake up in the morning and eat breakfast at 8am, your last meal of the day should be no later than 8pm.
After a few days or so, move to a 14:10 “brunch fast” window and work your way up to a 16:8 or even 18:6 plan. The key is to ease into it and tune in to how you are feeling on an hourly and daily basis.
For many, fasting is more manageable than expected, with decreased appetites being a typical marker of entering ketosis (21). Some people report feeling more energized, clear-headed, and focused after adapting to fasting regimens, though there is little research to support this in healthy adults (13, 22, 23).
The reason for extending the fast window over time is simple: the longer you fast, the more likely you’ll enter ketosis and induce autophagy. Autophagy is a natural, regulated process by which cells cleanse themselves, removing damaged components to make way for new ones, ensuring cellular health and efficiency, and indirectly supporting metabolism (24).
Fung says to expect results fast—in just a matter of weeks—on a combined keto and intermittent fasting plan. Once you’re where you’d like to be weight-wise, you can relax a little on the carb restriction and switch to a low-carb plan that’s less limiting than keto. “The main thing is to eat natural foods, less sugar, and less refined carbohydrates,” he says.
And there’s no need to lock yourself into a fixed fasting schedule. Keep it fluid and shake it up throughout the week, “It doesn’t mean you must do 16 hours every day. If for a little while, you do less, it’s OK, but if your weight goes up, you may want to do some more to compensate,” says Fung.
Many people wonder how long they can safely practice keto without causing harm to their bodies. While there is no set time limit, most experts recommend following the keto diet for a maximum of 6 months.
Generally, fasting can be practiced for periods of 48 hours or less without any major risks.
Longer fasts should only be done under the guidance of a healthcare professional to ensure proper nutrition and safety. If you encounter negative side effects, it is advisable to stop fasting.
If you are pregnant or breastfeeding, you should not follow a keto diet or practice fasting. Those with health conditions or taking medications should also consult with a healthcare professional before starting keto or fasting to ensure it is safe for them.
Keto and intermittent fasting both may help reduce inflammation, improve gut health, and encourage weight loss. When combined, the effect may be more pronounced. If you have a medical condition, talk to your healthcare team before starting keto, IF, or any diet plan.
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