Mar 30, 20223 min read

Can Intermittent Fasting Cause Weight Gain? [Intermittent Fasting Tips]

Can Intermittent Fasting cause weight gain and reverse your weight loss progress? Today, we're diving into the details of Intermittent Fasting and whether or not it can cause you to gain weight.

Can Intermittent Fasting Cause Weight Gain?

There are various forms of Intermittent Fasting, so to simply this response we'll be discussing the Time Restricted Eating method (TRE) of Intermittent Fasting. This means incorporating a daily fast of anywhere between 12 -22 hours per day and eating during the remaining hours of the day.

This type of Intermittent Fasting will not cause weight gain on its own. This isn't to say that you can't gain weight while Intermittent Fasting, rather if there is weight gain -- Intermittent Fasting likely isn't the cause.

For a bit of background, Intermittent Fasting can be an effective fat loss tool because it helps to keep the storing hormone insulin low during extended periods of the day. When insulin is low, it allows the fat burning process called lipolysis to be turned on. During the fast, insulin is low and therefore fat burning is turned on. This is also why Intermittent Fasting has been found to help with body recomposition, because it helps the body to primarily burn fat as fuel.(1)

The issue of weight gain with Intermittent Fasting comes in when you either:

fast too long or
break your fast wrong.

Let's dive into each of these concerns.

What Happens When You Fast Too Long?

Fasting "too long" is relative to each person. The main variable with fasting too long comes down to whether or not you're able to get all of your protein needs in for that day with your eating window.

Protein is highly satiating. When you eat protein, it causes the body to release the satiety hormone peptide YY. This strong satiety signal tells your brain that you're full, satisfied and don't need to keep eating. Peptide YY is so effective at shutting off hunger that it can be extremely difficult to eat high levels of protein at one meal.

If you don't eat enough protein throughout your eating window, this can result in a multitude of negative effects.

muscle loss
bone loss
increased hunger during your fast
hair loss

Specifically the increased hunger and muscle loss can work against your weight loss goals. Increased muscle mass is directly associated with increased insulin sensitivity.(2) As insulin sensitivity decreases, it becomes more difficult to use fat as fuel and can therefore make it easier to gain weight, specifically around the belly.(3)

If you're able to get all of your protein needs in during a 2 hour eating window (with a 22 hour fast), then you're not "fasting too long". However, if you're unable to get all of your protein needs in with your current fasting window (even if it's 18 or 16 hours), then you're "fasting too long".

Pssst - wondering what type of fasting is best for your goals? Click below for my free Intermittent Fasting Schedule quiz to find out!

What Happens When You Break Your Fast Wrong?

Another Intermittent Fasting "mistake" that can cause weight gain is breaking your fast wrong. As mentioned earlier, the main reason why Intermittent Fasting is an effective tool for fat loss is because it leads to periods of low insulin and increased fat burning. However, if you then break your fast and continue to eat throughout your eating window highly insulin spiking foods, then you can essentially "un-do" all of the low insulin spike perks from the fast.

For example, breaking a fast with fruit juice, toast and jam will massively spike the storing hormone insulin and shift the body into a state of fat storing. Do this enough throughout the eating window and this can entirely reverse your progress.

Instead, if you're looking to maximize fat loss with Intermittent Fasting, it's important to focus on less insulin spiking foods during your eating window. These include those rich in high quality sources of protein, fat and fiber. Great sources of protein, fat and fiber include:

greek yogurt bowl with nuts and raspberries
low sugar, high protein smoothie with chia seeds and peanut butter
chicken salad with avocado
a burger without a bun and a side salad

To sum it up, if you're experiencing weight gain with Intermittent Fasting, it's likely not the fast itself that's causing you to gain weight. Rather it's what you're eating (or not eating, in the case of protein) that can lead to weight gain.