Call it Intermittent Fasting (IF), alternate day fasting, 5:2 Diet, 4:3 Diet, 18-hour Diet, Every Other Day Diet, Fast Diet or Starvation Diet, but going without food for a period of time each week continues to gain attention in the scientific community.
Here at Wellness Nutrition Concepts, LLC, it’s no surprise I am not into fad diets or crazy concoctions that claim they’ll help you lose weight. I am more into the 80/20 philosophy—aim to eat right and make good choices about 80% of the time, but leave 20% room for indulgences and your favorite treats. So when I heard that people have been trying intermittent fasting as a way to lose weight, I was curious. Does this actually work? Is it safe? I researched whether or not intermittent fasting is good for you so I can tell you my honest opinion.
What Is Intermittent Fasting?
There are a number of types of intermittent fasting (IF): 5:2, 14:10, the eight hour diet. The key principle of all of these diets is that the eating pattern is ‘intermittent’, with periods of ‘semi-fasting’ or calorie restriction, interspersed with periods of eating. For example, in the recently popularized 5:2 diet, one eats as they ‘normally’ do for five days of the week, then restrict calorie intake to about a quarter of their estimated requirements, usually around 500-600 calories per day for two days of the week. The other option is time-restricted fasting, such as the 14:10 or eight hour diet, whereby you have designated eating periods and fasting periods within each day.
Fasting Window. You can choose a fasting window of which to not eat during the day, typically around 16 hours. Because you spend roughly 8 hours per night asleep (naturally fasting,) you’re then only required to tack on an additional 8 hours of fasting during the day. Many people choose to fast 4 hours before they go to bed, and 4 hours after they wake up—skipping breakfast. You can still drink water, coffee, and tea during your fasting hours.
Full 24-Hour Fast. You can do a full 24 hour fast once or twice a week, so from 7 pm Friday to 7pm Saturday, for example. You can once again still drink water, tea, or coffee during your fasting period. You return to normal eating after the fast is over, meaning you aim to consume the same amount of calories you normally would, not more, after you’re done fasting.
Why Do People Do Intermittent Fasting?
Here are the three biggest reasons for intermittent fasting that I’ve come across.
1) A Belief That It Burns More Fat
Some people believe that by fasting intermittently, you are able to reset your digestion, helping your body burn fat more effectively and ultimately lose weight. It takes about 6-8 hours to digest a meal. Some people think that by fasting for that amount of time, you then force your body to use stored fat—and not your food—as energy. The belief is that this burns up the fat instead of the food.
2) To Create a Calorie Deficit
By eliminating one meal out of your day, it’s suggested that you’ll create a calorie deficit. While it’s true that you need a calorie deficit (fewer calories going in than the amount of calories burned) in order to lose weight, if you are too hungry from fasting you can overeat at your next meals and end up eating just as many calories—if not more—than you would if you ate throughout the day.
3) A Desire To Retrain Your Appetite
Proponents of intermittent fasting will tell you that by doing this, you train your brain to only eat when you’re truly hungry, not by arbitrary times of the day (breakfast, lunch, and dinner). Some people claim that this can help people who tend to over-eat or binge-eat better identify when they are actually hungry. However, as noted above and as we’ll discuss in further detail below, fasting can actually cause “rebound overeating” in some cases.
- The overall energy restriction and hence weight loss will depend on the foods chosen when not fasting, so it’s not a free pass to eat poorly.
- The risk of entering into ‘starvation mode’ with severe energy restriction. This causes your body to increase the efficiency with which it uses energy and results in weight gain in excess of weight loss once an adequate energy intake is resumed.
- With a smaller total number of meals comes less opportunities to get essential nutrients in, so meals may need to be planned more carefully to avoid malnutrition and micronutrient deficiency.
- Designated fasting periods may make it difficult to participate in the social sharing of a meal.
- The psychological effects of this diet are unknown. Restriction of calories may be triggering for people with a history of disordered eating.
- There is no mention of healthy eating or exercise.
- May not work well for athletes or people regularly exercising as decreased energy levels may be experienced during fasting periods.
- This is not for everyone and may even be dangerous in certain conditions such as diabetes mellitus or pregnancy.
What I Think About Intermittent Fasting
There is no one-size fits all approach to nutrition. Our bodies have different needs. Some of us are sensitive to dairy or gluten, while others may be deficient in things like iron or magnesium. Some people are comfortable going long stretches without eating, while others feel the effects of low blood sugar a few hours after a meal. Finding the nutritional strategy that works for you is all about identifying what makes your body feel good and operate most efficiently.
As a dietitian however, the concept of fasting does not make me think “fat loss.” What proponents of intermittent fasting might not realize is that fasting doesn’t cause your body to break down only fat. When you don’t consume carbohydrates after about six hours, your body will begin to convert some lean tissue (meaning muscle) into carbohydrate as well. Your metabolism needs fuel in order to work efficiently. When you starve your body, your metabolism shuts down to conserve energy. In some fasting cases, you’ll burn less fat than if you actually fueled your body with healthy food regularly, because glucose must be present for body fat to burn.
Here’s what I suggest for people to stay healthy and burn fat:
Eat a healthy diet of sensibly portioned meals comprised of veggies, fruits, nuts, seeds and healthy fats, lean protein, whole grains and dairy.
Incorporate both cardio and strength training into your workout routine. Strength training builds muscle, and muscle is a more metabolic tissue than body fat. This means that the more muscle you have, the more calories you’ll burn daily, even at rest.
This is what we want for both fat burn and long-term health: a metabolism that runs efficiently—not one that’s constantly going into starvation mode. Have you tried intermittent fasting? What works best for you? Let me know in the comments below!
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