I've been a trainer and health coach for almost 10 years. The vast majority of my clients are female, and most of them also have serious weight-loss goals in mind. Because intermittent fasting (IF) has become so popular, I get a lot of questions about whether it's a good idea to implement it into a daily diet for weight loss. My answer is usually no. IF is a method of periodic fasting that's paired with a window of eating. For example, 16:8 IF is the most popular type, and it's structured by a 16-hour fasting window followed by an 8-hour eating window. In other words, you would eat all your meals between 12pm - 8pm, and fast the rest of the time.
Don't get me wrong, there are some proven benefits to IF, such as improved blood pressure and less brain fog. But if your goal is weight loss as a woman, I generally advise against IF for a few different reasons. I happily recommend IF later on when you've reached your goal weight because you might find that you'll benefit from it, but if you're dead set on fat loss, these are the reasons I don't recommend IF.
It's Extremely Difficult To Fit In All the Protein You Need To Eat
One of the most common mistakes I see women make when they're trying to lose weight is undereating. They don't eat nearly as much protein (or carbs, for that matter) as their body needs, which actually sabotages your weight-loss efforts. When women talk about losing weight, what they actually want is a change in body composition; they want to look more lean, toned, and fit. And the way we accomplish that is by eating enough protein in order to build lean muscle, which in turn burns fat faster and boosts your metabolism so it works more efficiently. If you aren't eating enough protein, you won't be able to build the lean muscle you need to get those results.
If you aren't eating enough protein, you won't be able to build the lean muscle you need to get results.
So when I assign women their protein goals, they're usually shocked. They can't believe that they have to eat 160 grams of protein in a day. If you think it's difficult to eat that much protein in a whole day, how much more difficult do you think it's going to be to eat that much in eight hours? This is why IF sets women up for failure who need to shed fat, which is only done by building lean muscle to boost your metabolism. Portion control and a few meals throughout the day is a much easier way to achieve your protein goals, and it's impossible to use that in conjunction with IF. Besides, experts say that IF can actually lead to lean muscle loss, which is completely the opposite effect we want.
Your Hormones Could End Up Working Against You
We already know how different women's bodies are from men's, especially when it comes to hormones. Short-term fasting increases cortisol (the stress hormone) in the body, and this leads to increased insulin resistance and fatigue, as well as causes a decrease in the conversion of thyroid hormone over time. All of this will make your body hold onto fat and store it, rather than shed it.
Short-term fasting increases cortisol in the body.
Additionally, because it's so easy to undereat when you're doing IF, that could cause a caloric restriction that results in menstrual disorders because your hormones are all out of whack. None of this makes for a good weight-loss environment.
In my experience, clients who have had hormonal issues or menstrual disorders actually find a lot of relief from negative symptoms and achieve fat loss at a faster rate when they eat small meals and snacks throughout the entire day.
It's Much Easier To Overeat or Emotionally Eat
When you haven't eaten in 16 whole hours, you can get hangry. The kind of hangry that makes you cranky, tired, and even emotional. When you get to this point, self-control is much harder to find, so you end up reaching for whatever is in front of you, whether it's a dessert or fast food or something processed. Women especially have a difficult time with emotionally eating or overeating in general, which is why I don't recommend IF for weight loss. If you're really trying to shed fat, it's not helpful to go for a long period without food because that makes you much more likely to binge eat or at the very least make poor choices with what you end up eating.
When you haven't eaten in 16 whole hours, you can get hangry.
This creates an unhealthy cycle of bingeing then fasting, bingeing and fasting. This yo-yo effect makes it much harder for your body to lose fat, so you're stuck in this cyclical pattern that doesn't produce good results. My clients have found much better results by eating regularly throughout the day and enjoying a small dessert at night when they're not ravenous.
Make whatever decision is best for you at the end of the day, but from my personal experience and my experience as a coach, IF is best reserved for people who have very specific health goals in mind that don't necessarily prioritize weight loss. It becomes much easier to control your food intake when you're eating regularly throughout the day, and you want to develop a healthy relationship with food in the long run so that your weight loss is sustainable and long-term.