Combining Keto and Intermittent Fasting Might Be the Fastest Way to Torch Fat
- By Alicia Tyler
- Fact-checked by Joy Ferguson
- June 27, 2023
Fast Facts
- Both the keto diet and intermittent fasting have been linked to weight loss.
- Combining keto and intermittent fasting may lead to greater weight loss as well as reducing inflammation and improving gut health.
Nearly half of Americans report gaining weight since the start of the pandemic (1). Not surprising, given stress (2), and social isolation (3) both may be linked to weight gain. 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, and improve gut health—and when done in tandem—may have a significant impact on weight loss, in less time than if you opt for just one of the two.
Here’s how to start keto and intermittent fasting to reduce body fat fast.
What Is The Keto Diet And How Does It Work?
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 (4), 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 (5), may help enhance cognitive function, (6) and may help stabilize blood sugar (7).
Scientists initially developed a ketogenic diet with the primary purpose of aiding in the management of seizures in children suffering from epilepsy.
Keto Facts
- Your body normally burns carbohydrates for energy.
- On the keto diet, you limit the amount of carbs you eat. This causes your body to burn fat instead.
- This switch has been linked to lower inflammation, better cognitive function, weight loss, and stablized blood sugar.
What Is Intermittent fasting (IF) And Why Do People Use It?
Intermittent fasting (IF), is exactly what it sounds like: splitting your 24-hour day into feeding and fasting windows.
Many experts recommend starting with a 12-hour fast to 12-hour eating schedule 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, Ph.D., CNS. This is called time-restricted eating.
There are other fasting regimens, including
- Alternate-day fasting, where you fast one day and eat normally the next
- One meal a day (OMAD), fast for 23 hours a day and eat for just 1
- Eat Stop Eat, where you abstain from food up to two days in a week.
- 5:2 where you eat normally for 5 days and then restrict your caloric intake to around 500 calories for two days.
- The Warrior Diet where you eat one main meal, feasting in a four hour window at night, as well as fasting for 20 hours sustained with only small portions of foods such as raw fruits-and-veggies throughout the day.
No matter what fasting regimen you choose, after several hours without eating, a process called metabolic switching kicks in. Your body depletes its insulin levels and starts to burn fat for energy, similar to the shift that occurs 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:
- May help to prevent, treat, and reverse insulin resistance, a condition that may put you at higher risk for a slew of diseases from cancer to Alzheimer’s to heart disease, and more
- May help to reduce inflammation in the body, which can lower your risk for many age-related conditions and diseases.
IF At a Glance
- Intermittent fasting (IF), involves splitting your 24-hour day into feeding and fasting windows.
- There are multiple fasting regimens, based on the length of the eating and fasting windows.
- When you fast, your body starts to burn fat for energy.
- In addition to weight loss, IF is linked to improved insulin resistance, reduced inflammation, and more.
The Benefits of Pairing Keto Plus Intermittent Fasting
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 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:
Weight Loss
“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 fasting 16 hours a day, an average may be about one to two pounds per week, faster at the start and then slowing down.”
Lower Insulin Resistance
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, which increases blood sugar and eventually may lead to health issues like diabetes, obesity, high blood pressure, and high cholesterol.
On a combined keto and intermittent fasting plan, not only are you not consuming any food for extended periods—therefore blood sugar can’t spike during the fasting time—but when you do eat, you’re consuming a very low amount of carbohydrates.
The very low-carb nature of keto means glucose levels remain steadier than on a typical standard or moderate-carb diet.
One study (7) found that people with type 1 diabetes who followed a very low carbohydrate diet had significantly improved blood sugar control. Additionally, incorporating occasional fasting into your keto diet regimen can enhance the results for individuals aiming to control their blood sugar levels, whether to prevent prediabetes or reverse type 2 diabetes.
Lower Inflammation
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. Being in ketosis means your liver is producing and releasing ketones which in some studies have been linked to a reduction in oxidative stress (8).
Studies also suggest that Intermittent fasting may reduce inflammatory activity. According to a study led by researchers from Mount Sinai, when people fasted for a short period of time, the amount of pro-inflammatory cells called “monocytes” into the bloodstream was reduced (9). During periods of fasting, these inflammatory cells went into sleep mode and were less inflammatory than monocytes found in those who were fed. (10, 11).
Improved Cognitive Health
Research into the brain benefits of IF are beginning to show promising results. Improved learning, memory, mood and mental focus are some of the potential benefits that studies have begun to suggest from fasting (12, 13).
Research (14) 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.
One study (15) examining fasting and weight loss revealed that people who practiced IF for eight weeks experienced noteworthy improvements in their emotional well-being and depression compared to the control group.
On the keto side, though research remains preliminary, there’s some evidence to suggest that a ketogenic diet may be beneficial to those with Alzheimer’s disease. Emerging research (16) 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 (17) by helping to ease depression and stabilizing mood.
Pairing Keto and IF
Combining keto and intermittent fasting may help you lose weight, keep glucose levels stable, ward off conditions related to inflammation, and improve your memory.
The Risks Of IF And Keto
“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.
Who Shouldn’t Consider Intermittent Fasting?
- People with diabetes or blood sugar problems
- Anyone on blood pressure or heart-health medication
- Anyone with a history of an eating disorder
- Individuals who are underweight or struggling with weight gain
Expect results fast—in just a matter of weeks—on a combined keto and intermittent fasting plan.
How To Get Started With Keto And Intermittent Fasting
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.
Step 1: Reduce your meals and eating window and find your keto style
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).
If you prefer a more vegetable-forward plan, consider Ketotarian: The (Mostly) Plant-Based Plan to Burn Fat, Boost Your Energy, Crush Your Cravings and Calm Inflammation. If you’re more of a carnivore, check out Keto Carnivore Cookbook: Low-Carb Recipes, Tips, and a 6-Week Meal Plan to Boost Your Diet Success.
Because IF typically, 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).
Step 2: Start Phase 1 Of Your Meal And Fasting Plan
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 many reporting decreased appetites (18) and feeling more energized, clear-headed, and focused (19). The reason for extending the fast window over time is simple: the longer you fast, the more you can restrict your daily caloric intake and allow your digestive system a break allowing reparative functions.
Aim For Long-term Fasting Flexibility
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.
The Bottom Line
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.
References
1. Jagdish Khubchandani, et al (2022) COVID-19 pandemic and weight gain in American adults: A nationwide population-based study.
2. Koski M, Naukkarinen H (2017) The Relationship between Stress and Severe Obesity: A Case-Control Study.
3. Hajek A, Kretzler B, König HH (2021). The Association Between Obesity and Social Isolation as Well as Loneliness in the Adult Population: A Systematic Review.
4. Chaudhry R, Varacallo M. Biochemistry (2021) Glycolysis
5. Xiangjun Dou, et al (2022), Evaluation of the seizure control and the tolerability of ketogenic diet in Chinese children with structural drug-resistant epilepsy.
6. Rusek M,et al (2019). Ketogenic Diet in Alzheimer’s Disease.
7. Lennerz BS, et al (2018) Management of Type 1 Diabetes With a Very Low-Carbohydrate Diet.
8. Youm YH et al (2015). The ketone metabolite β-hydroxybutyrate blocks NLRP3 inflammasome-mediated inflammatory disease.
9. Jordan S et (2019). Dietary Intake Regulates the Circulating Inflammatory Monocyte Pool.
10. Youm YH et al (2015). The ketone metabolite β-hydroxybutyrate blocks NLRP3 inflammasome-mediated inflammatory disease.
11. Inflammation; What Is It, [Fact Sheet]
12. Karin Seidler, Michelle Barrow (2022). Intermittent fasting and cognitive performance – Targeting BDNF as potential strategy to optimise brain health.
13. Gudden J, et al (2021). The Effects of Intermittent Fasting on Brain and Cognitive Function.
14. Walter Currenti et al, (2021). Time restricted feeding and mental health: a review of possible mechanisms on affective and cognitive disorders.
15. Fitzgerald KC, et al (2018). Effect of intermittent vs. daily calorie restriction on changes in weight and patient-reported outcomes in people with multiple sclerosis.
16. Rusek, Marta et al (2019). Ketogenic Diet in Alzheimer’s Disease.
17. Brietzke E et al (2018). Ketogenic diet as a metabolic therapy for mood disorders.
18. Elizabeth F. Sutton, et al (2018). Early Time-Restricted Feeding Improves Insulin Sensitivity, Blood Pressure, and Oxidative Stress Even without Weight Loss in Men with Prediabetes.
19. de Cabo R, Mattson MP (2020). Effects of Intermittent Fasting on Health, Aging, and Disease.
