Intermittent fasting (IF) is an eating pattern that cycles between periods of fasting and eating. It’s grown into one of the most popular health trends due to its many benefits—IF has helped many to lose weight, reduce inflammation, improve mental clarity, live longer, and more. You might be thinking, where do I sign up?
But while intermittent fasting is healthy for some, it may be problematic for others, even dangerous. This article breaks down intermittent fasting, how it works, and the many ways to do IF, and addresses what groups should proceed with caution or avoid IF altogether.
What is ‘IF’ ALL ABOUT?
One of the main benefits of IF is improved metabolic flexibility, which has to do with the body’s ability to use carbohydrate and fat for energy. When given a choice between these two fuel sources, the body chooses carbohydrates first because they convert into quick and easy energy. But carbohydrate-based energy is short-lived and causes blood sugar levels to quickly rise and fall. When the body gets stuck in the cycle of blood sugar highs and lows, it requires more fuel and craves sugary snacks. This pattern of eating keeps insulin levels elevated and causes the body to convert any unused carbohydrates into fat. So by staying in this carbohydrate-based state, where the body is prone to frequent snacking and increased fat storage, the body can become resistant to weight loss.
But when we go for long periods of time without eating, our bodies tap into stored fat for energy. By improving the body’s tendency to use body fat for fuel, we become “fat adapted,” and it’s easier to lose weight. This is how the IF lifestyle helps many shed stubborn and unwanted pounds.
The benefits don’t end there. When the body burns fat for many hours, it eventually moves into a state called ketosis, where ketone bodies are made and used for energy. Ketone bodies are the byproducts of fat burning, and science shows that higher levels of ketone bodies in the bloodstream can lead to longer-lasting energy, lower blood pressure, better insulin sensitivity, cognitive enhancement, and an improved mood.
How Does IF Work?
There are a number of different ways to do IF. Some of the most popular methods are described below.
16:8 approach: Fast for 16 hours, and eat your meals during an eight-hour eating window. Among intermittent fasters, it’s common to begin eating in the afternoon (i.e., 2 - 10 pm), but research suggests that an earlier eating window can lead to better results (i.e., 7 am - 3 pm). Many also claim that they have better results with other variations of this approach (e.g., 12:12, 14:10, 18:6).
Alternate-day fast: Fast for 24 hours once or twice a week. For example, you would begin your fast directly following dinner on one day, and you wouldn’t eat until dinner the next day.
5:2 approach: Consume only 500–600 calories on two non-consecutive days of the week, but eat normally for the other five days.
There are many other ways to do IF (e.g., spontaneous meal skipping or eating one meal a day), but there’s little to no research on their effectiveness. When it comes to choosing a method, go with what works for your lifestyle—the last thing you want to do is increase your stress levels during a fast. Whatever you choose, keeping a consistent schedule can help maximize positive results.
More Tips on IF
Though none of the various IF methods specify which foods to eat, fasting should always be combined with a healthy diet and lifestyle. Binging on junk food during the eating window is detrimental, as your body requires quality nutrition after a fast.
Exercise is an important part of an IF lifestyle and can help maximize the benefits; however, IF may not be effective for those working to improve performance or build muscle.
The benefits of IF aren’t likely to last when you stop the practice and resume previous eating habits.
Can IF Be Harmful?
Overall, IF seems to be a promising dietary practice for losing weight and supporting overall health, but it may not work for everyone. Some groups are more likely to experience complications from restrictive eating and should not attempt IF unless under the close supervision of a physician. These groups include the following:
People with advanced diabetes or people taking diabetes medication who need to maintain steady blood sugar levels to stay healthy
People with a history of eating disorders, such as anorexia and bulimia, that could potentially be triggered by restrictive eating practices
Endurance athletes requiring a steady supply of calories and nutrients to train, perform, and recover
People who are underweight or struggling to gain weight (people in this category should focus on increasing fat storage, not using it)
Pregnant or breastfeeding women who have increased calorie and nutrition needs that IF likely won’t provide
There’s some evidence suggesting that IF can be more problematic for women than men. One study showed that IF improved insulin sensitivity in men but worsened blood sugar control in women. However, there’s very little research that supports this study’s findings.
Here’s what we do know—restrictive eating can disrupt female reproductive hormones, namely estrogen and progesterone. These hormones play a key role in regulating ovulation, metabolism, and mood. For women with known hormone imbalances, fertility issues, or those that are trying to conceive, IF is not advisable. People with stress disorders or chronically high cortisol levels should also proceed with caution since food restriction can further increase stress and cortisol levels. But it’s also worth mentioning that a documented benefit of IF is decreased insulin resistance, which may be important in mitigating the dangers of chronic stress. Ultimately, more research is needed to understand the long-term impact of IF on hormones and stress regulation.
So for Now...
It seems clear that IF isn’t for everyone. But if you find yourself in one of the at-risk groups, you don’t have to miss out on the benefits of weight loss, increased energy, and improved focus. You can still experience those benefits by committing to a healthy, well-balanced lifestyle—eat more plants, choose healthy fats and lean animal proteins, drink water, and avoid added sugars and processed foods. Sticking to this kind of diet is what will have the biggest impact on your health.
If you’re thinking about giving IF a try, it’s a good idea to do some self monitoring—by collecting data on your health, you can better understand how IF affects you. A good place to start is daily journaling to record your stress levels. Having elevated stress levels over the course of several days and weeks means that IF may not ultimately benefit you. Ask your doctor for more advice on how to determine if IF is right for you.
References
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