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Intermittent fasting (IF) has become a popular weight-loss strategy, as well as an entry point for dieters into the world of ketogenic eating and other advanced nutrition strategies. Intermittent fasting involves limiting the window of time in which you eat—normally to a period of anywhere from 16 to 24 hours.
For example, you might fast from dinner on Monday until lunch on Tuesday, or skip breakfast on Mondays and Tuesdays. As with any nutrition strategy, there are pros and cons to IF. On one hand, it can be an effective tool for reducing body fat and promoting fat loss. On the other hand, IF is not right for everyone.
Depending on your genetics and your particular health goals, some people will get much greater benefits than others from IF.
What happens to your body when you fast?
When you fast, your body goes into “survival mode,” shifting its primary focus away from supporting and building new cells towards preserving and storing what it already has. During the initial period of fasting, your body burns glycogen, a form of stored sugar that’s found in the muscles and liver. Once glycogen is depleted, your body turns to burning fats for fuel.
This is called “ketosis,” and it’s what happens when you’re eating a low-carb, high-fat (LCHF) diet. Depending on the length of the fast, you may also experience a reduction in blood glucose and insulin levels, as well as an increase in growth hormone and other appetite-regulating hormones.
How does intermittent fasting benefit your body and brain?
While fasting, your body also benefits from lower levels of inflammation, better hormone regulation, and optimized insulin sensitivity. The benefits of fasting include:
Increased insulin sensitivity
Increased growth hormone
Improved focus Note that IF has been shown to have many benefits for both your brain and body even in short-term fasts of under 24 hours. These benefits continue to accrue over the long term as you use intermittent fasting as a regular diet strategy.
What happens to your brain when you stop fasting?
When you stop intermittent fasting, your brain goes into a minor “withdrawal,” experiencing a decline in cognitive function similar to what happens when you stop taking certain medications.
You may experience a drop in mental clarity, mental focus, and mood as your brain adjusts to being fed regularly again. The decline in mental function caused by stopping IF is a very minor and temporary effect, not a long-term consequence.
Is IF bad for your brain?
There’s some evidence that IF may have a negative effect on certain people’s long-term cognitive ability. For example, people with a genetic mutation called HCRTR2 have been shown to experience decreased cognitive ability after periods of fasting.
While IF may not be ideal for everyone, it’s important to remember that even the most effective nutrition strategies are designed to be temporary. If you’re using intermittent fasting to lose weight, your goal is to be on a normal, balanced diet once you’ve reached your desired weight.
What are the other side effects of intermittent fasting?
There are a few potential side effects of intermittent fasting. The most common is hunger, which is a normal part of the metabolic process of fasting. Hunger and cravings are less intense in people who are fully keto-adapted, but they are inevitable during the initial stages of an IF eating schedule.
Another possible side effect of IF is poor sleep, caused by hunger, cravings, or a drop in cognitive function. Finally, some people experience an “over-recovery” on IF, gaining weight faster than they would otherwise. This effect is rare, but it can happen to hyper-responders.
From the research we have so far, intermittent fasting seems to be a safe and effective weight-loss strategy. It also offers a range of health benefits and a decrease in instances of cognitive decline.
If you’re interested in trying intermittent fasting, there are a few things to keep in mind. First, you should be sure to eat a high-fat diet, as this will help you “get into ketosis” faster.
Second, make sure you’re getting enough sleep, and try to manage your cravings with healthy snacks and non-nutritive beverages like coffee.