What You Should Know About Intermittent Fasting Heath Claims
I want you to get the results you want in your body without being confused about all of the options out there. Today we're talking about what's going on behind the amazing headlines and health claims of intermittent fasting (IF). I want you to be able to decide if IF is truly something you want to experiment with or if there are better options.
There's a difference between what's statistically significant versus actually significant to you.
One of intermittent fasting's big appeals is that it's great for weight loss. Let's talk about what "weight loss" means. Most of the studies done in humans are only about 8-12 weeks. The average weight loss (if any) reported in IF studies was about about 2-3 pounds over that 2-3 month period of time. Note most of these studies are done with overweight or obese populations - individuals who have weight to lose.
It's always important to look beyond the headlines to understand what they truly mean. Is the level of restriction with intermittent fasting worth that amount of weight loss for you? You can achieve much faster results while feeling more energized and satisfied by focusing more on WHAT you're eating versus WHEN.
In some cases, a large portion of weight loss was muscle loss.
Two of the intermittent fasting claims are that it's great for boosting metabolism and burning fat. After a 10-12 hour break from eating, there are certain pathways that get turned on that help to start burning fat. There are also studies backing up that intermittent fasting resulted in just that. However when you look closer, in some cases a significant amount of that weight (67%) was lean muscle mass. I'm guessing you're wanting to lose fat not muscle. Muscle is great for boosting your metabolism and helping you feel strong.
Why are there conflicted results?
It's complicated! It's not just about the time that you're eating. There are so many other factors that influence your metabolism, weight loss, and overall health.
There was a study done in a population of healthy men demonstrating that the intermittent fasting group could burn fat while maintaining muscle. These men already had an established strength and resistance routine. The study also controlled the number of calories between the fasting and control group.
However, one thing that wasn't highlighted is that those men did have a decrease in their testosterone levels. That's an important thing to consider. If you are a busy professional trying to lose weight, don't you also want to have good energy levels? It's hard to say what the long term implications of the drop in testosterone would be or if that would have persisted if the study had been extended.
Ultimately, this is why I really recommend only dabbling in intermittent fasting if you already have a great relationship with food and you're managing your stress well.
IF May Negatively Impact The Food You Do Eat
One huge appeal with intermittent fasting is it's simple! You don't have to change what you're eating at all. Sometimes when something sounds to good too be true, it is. Sure you can continue to eat what you're eating, but there is no way you'll optimize the way you feel physically and mentally. There's also the potential that fasting is going to negatively influence the way you're fueling your body during the feeding window.
Often I see that once people make it to their eating window, they feast. You're hangry and you deserve a lot of food because you've restricted yourself! When you go to the grocery store starving how many things end up in your cart that you weren't intending to purchase? IF can have the same effect.
At the same time, that shorter eating window often results in less protein and nutrient-dense food like vegetables. Those foods are really important for your overall longevity, health, and metabolism. That decrease in protein is likely one component leading to muscle loss that is sometimes seen.
Intermittent Fasting Might Decrease Your Motivation to Move
In some cases, intermittent fasting led to significantly decreased overall activity (30%!) compared to their baseline. Movement is a really amazing way to lose weight and burn fat. But it also has a great side effect of boosting your mood and motivation! These results indirectly suggest that IF may not be resulting in optimal energy levels.
Any time you're changing your diet, it's important to look at the big picture.
How is this affecting all aspects of your lifestyle and overall health? You may be losing weight, but at what price?
- Are you feeling "hangry"?
- Are you missing out on events with family or friends because it's not within your eating window?
- Are you constantly thinking about when you will be able to have your next meal?
- Are you finding it hard to concentrate or feel energized during the day?
You want something that is going to get you results while also being enjoyable and sustainable, right?
I would love to see more details about the individuals who drop out of IF studies. Of course, with all studies it's expected that some participants will drop out. And there are lots of factors for why that happens. But it's important to remember that the results and claims you hear about weight loss and overall health only include the individuals who completed the study.
If you're interested in how many people start intermittent fasting AND stick with it long enough to see results that's likely not going to be as impressive. I would love to see a long term (at least 1-2 year) study looking at this in humans.
Intermittent Fasting Boosts Longevity...in Mice
The longevity and anti-aging health claims for intermittent fasting are very attractive and may have a lot of truth behind them. However, we don't know that for sure yet.
As a high performance health coach AND veterinarian, I would just like to point out that mice and rats are not small humans. While mice are excellent models for starting to explore ideas that might be true in humans, those results are not directly correlated. We need long term studies performed in people before we can feel confident about these health claims, and we don't have those yet.
Many of the things that might be sacrificed with intermittent fasting (eating nourishing food, being active, connecting with others, happiness, etc) are really important for longevity and overall health. Yes, intermittent fasting may be an amazing way to turn on pathways that help to improve lifespan, but at what price? If many other positive behaviors are being sacrificed for that one way of eating, what is the overall impact on your health and happiness?
Any time you want to experiment or make changes in your diet, I really encourage you to listen to your body and see how you feel.
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