Dr. Anthony Gustin is a board-certified sports chiropractor, functional medicine practitioner, entrepreneur, podcast host, and founder of Perfect Keto.
If you ever wondered if fasting could help you lose weight, you came to the right place.
Many individuals use fasting to benefit their health and speed up weight loss. However, it important to do it safely and in a way that sets you up for success.
To get a clear picture of how intermittent fasting can affect weight loss, you must first understand what Intermittent fasting is, and what its benefits are – but also its risks.
Intermittent fasting — the most popular form of fasting today — consists of eating within a specific window of time in the day, and not eating for the remaining hours of the day. For example, one popular version of intermittent fasting is the 16/8 method. This entails a nonfasting window of eight hours (such as 11am to 7pm) followed by a fasting period.
Intermittent fasting methods vary from person to person, depending upon his or her goals. Some individuals practice fasting for longer periods, alternate-day fasting or 24-hour fasts once or twice per week. A more moderate approach is an overnight fast, where an individual simply eats dinner earlier and breakfast later the following morning.
Benefits of Intermittent Fasting for Weight Loss
Individuals use intermittent fasting to lose weight fast. In studies done by the NIH, there was reported weight loss with over 84% of participants — no matter which method of fasting they chose (alternate day fasting, the 8/16 method, or another approach)[*]. Science has shown intermittent fasting to be an efficient weight loss tool, sometimes more than simply cutting calories. In one study, intermittent fasting was shown to be as effective as continuous calorie restriction in fighting obesity[*].
Intermittent fasting has been shown to increase fat loss while maintaining lean muscle mass. In one four-week study, researchers concluded that a fasting diet resulted in greater weight loss — while maintaining muscle mass — than participants following a low-calorie diet. This happened even though the total calorie intake over the four weeks was similar in both groups[*].
When following a ketogenic diet, fasting can help you enter ketosis, the desired metabolic state for weight loss and fat burning, more quickly. The longer you remain in a healthy state of ketosis, the better. Following a ketogenic diet while practicing intermittent fasting can help keep you in ketosis, even after breaking a fast.
There are many reasons to practice intermittent fasting outside the realm of weight loss. Research has shown fasting can help improve cardiovascular risk[*], reduce cholesterol levels[*], and reduce inflammation[*]. Other individuals report improved cognitive benefits.
Intermittent Fasting and Disease
Intermittent fasting may help improve your risk of multiple diseases, improve your overall health, and even slow down the aging process (who doesn’t wish for that?)[*]. Time and time again, intermittent fasting has shown to help improve cardiovascular risk and slow the progression of Type II diabetes[*].
Have you ever wondered why your doctor asks you to fast before a blood test? While fasting, your body can lower its glucose and insulin levels, improve its blood pressure and rate, and improve lipid levels [*]. Fasting has been shown to slow or prevent the onset of many diseases, from cardiovascular to respiratory. For example, in one study individuals with asthma who experimented with intermittent fasting not only lost weight, but showed improved symptoms of their asthma[*].
Intermittent Fasting and Hormone Levels
Intermittent fasting can help maintain healthy hormone levels, including human growth hormone, insulin, and norepinephrine:
- Healthy human growth hormone levels help with muscle and bone growth, fat loss and metabolism of sugar and fat.
- Insulin levels increase whenever you eat. By fasting, you’re able to decrease insulin levels and enter a fat-burning state.
- Norepinephrine helps break down fat cells to be used for energy, thus facilitating ketosis.
Intermittent Fasting and Mental Health Benefits
It seems intermittent fasting can help your mind as well as your body. Fasting has been shown to help improve your memory, reduce oxidative stress, and preserve learning function[*]. Some researchers believe that because humans went thousands of years where food was not readily available, they adapted to function at a high-level (both mentally and physically) while in a food-deprived state[*].
There are several theories as to how fasting helps improve cognitive function. Some scientists believe that because your cells are under mild stress while fasting, it helps improve their function. Your cells adapt to this stress by enhancing their own ability to cope, which helps you focus more intently.
This is similar to the stress your body undergoes when you hit the gym. While exercising, that is a form of stress your body endures. As long as you give your body enough time to recover afterward, it will do your body good. The same applies for intermittent fasting — as long as continue to alternate between regular eating habits and fasting, it will continue to benefit you[*].
Finally, when you go long periods without food, it causes your body to release ketones into your body. This has been shown to improve memory and learning ability, as well as slow down diseases in the brain[*].
To those who find calorie restriction or constant dieting stressful, intermittent fasting is an appealing alternative. Some studies show that patients actually preferred fasting to constant calorie restriction[*
While going entire days without food may seem to go against everything you’ve been taught about health and nutrition, some studies there are no adverse mental or physical effects through fasting[*]. Depending upon the approach you take, you may find that a prolonged fast can become quite uncomfortable. For example, when studying individuals taking various approaches to intermittent fasting, the NIH found those who attempted alternate-day fasting reported great feelings of hunger. More so, those who tried the alternate-day fasting method did not lose significantly more weight than other groups[*].
Conventional nutrition says that in order to lose weight fast and keep your metabolism high, you should eat six meals throughout the day. This logic implies that our metabolic rate will slow if we go too long without eating, causing us to store fat.
While the idea of frequent snacks might be appealing to some, the science is painfully outdated. Eating every few hours does not give our bodies time to digest. In fact, fasting for short time periods can actually raise our levels of fat burning.
One concern with fasting that still seems undecided is the effect it has on those with diabetes or similar diseases. Typically, those who are diabetic eat meals every few hours to maintain blood sugar levels, making intermittent fasting next to impossible. While evidence surrounding diabetes and fasting is still growing, one recent study actually showed intermittent fasting helped those with Type II diabetes lose weight and improve fasting glucose[*].
If you’re new to fasting, consider starting small. A moderate approach — such as an overnight fast — will help you adapt. When your body gets used to it, move to an 8/16 fasting diet or alternate-day fasts. This way, you won’t be overwhelmed with the transition.
To help you begin your journey with fasting for weight loss, a few tips are helpful:
- Focus on consistency. Pick one method of fasting, and stick with it long enough to experience the full effects. Change is uncomfortable at first, and it involves an adjustment period.
- Focus on quality. Even though you’ll likely be eating fewer calories overall, the foods you eat are still important if you want to lose weight — and keep it off — healthfully. For some ideas, see our ketogenic diet food list and list of foods to avoid on a keto diet.
- Stay hydrated. Don’t forget to drink water. It’s important to stay hydrated when fasting since it is the only thing you can consume during that time.
- Check your level of ketosis. If your goal is to fast while in ketosis, make sure you continue to check your ketone levels. See our guide for testing your ketone levels for the correct way to measure.
And remember: Fasting for a certain length of time is no excuse to binge on candy, soda, and fried foods afterward. No matter what type of fasting you try for weight loss, it’s important to focus on healthy, nutrient-dense and high-fat foods outside of fasting periods. Fasting helps your body “reset.” Don’t hinder your own results by returning to unhealthy foods.
Fasting for Effective Weight Loss and Fat Loss
Overall, intermittent fasting can be a great tool to lose body fat and body weight. It can also be a mentally-positive alternative to those who struggle with calorie counting and portion control.
The key with fasting — as with any weight loss plan — is to find what works for you. Focus on healthy foods in between fasts, and remind yourself that you are taking control of your body, health, and future.