I’m always surprised (and a little frustrated) by the staying power of certain ideas within the health and fitness world. Some concepts just get lodged in people’s brains and have an incredible amount of influence over them.
One of the most persistent and pervasive dietary doctrines out there is the thought that you absolutely need to eat 5 or 6 small meals each day. Doing so, the proponents says, will essentially stoke the fires of your metabolism, keeping it running as fast as it possibly can go.
And this bothers me.
Why? Because not only is it blatantly wrong, according to mounds of research, it is also counter productive.
The real problem with this myth is that it goes a step further. In addition to encouraging these mini-meals for increased fat burn, it tells people that if they skip meals or—horror of horrors—fast, they will actually be hurting their metabolism.
[Related: The #1 Cause of a Slow Metabolism]
The truth, though, is that intermittent fasting for fat loss is a powerful and effective strategy. And anything that detracts from it is essentially creating a roadblock between people and their goals.
That’s where my issues come from.
So far, however, I’ve made lots of strong, opinionated statements and presented little actual evidence. As you know, that’s not how I like to do things. This just gets me all fired up.
Let’s take a step back, then, and look at the science surrounding this whole topic to see why I am so very confident in the usefulness of intermittent fasting for fat loss.
Intermittent Fasting for Fat Loss and the 5-Meal Problem
Okay, so let’s revisit the claims of the 5-mealers. Namely, this approach is supposed to speed up your metabolism based on something called the thermic effect of food.
This is absolutely a real thing. Whenever you eat, your body has to expend energy in chewing, swallowing, digesting and metabolizing your meal. That much is true.
Here’s the thing: that effect accounts for only about 10 percent of your total caloric expenditure on any given day. That really isn’t much.
When it comes to weight control, the real issue of concern is your resting metabolic rate (RMR). This measures the amount of calories your body burns when you’re at rest and not doing anything at all. Your RMR makes up about 70 percent of your total caloric expenditure.
This is the main point: There is no evidence to suggest that the frequency or even the size of your meals has any impact on your RMR. In fact, numerous studies have found that there is no difference in weight loss when you cut up your meals in any specific way. (1)
These researchers have looked at this thing from every angle. They’ve messed with the timing, macronutrient profile and size of meals – all to no avail.
How often you eat has little impact on your resting metabolic rate and, therefore, on your long-term weight control.
But what about the idea that skipping meals or going too long between them can slow your metabolism down or even cause it to sort of reverse – like when doing a 1-day fast?
In theory, this actually makes sense. The idea is that the human body will eventually hit a “starvation mode” as a survival tool that will stop you from losing any more weight and, in its panic, start to add fat to your frame.
While this might look feasible on paper, it just doesn’t hold up to scientific scrutiny. In one famous (and kind of scary) study called the Minnesota Starvation Experiment, researchers gave subjects only about 50 percent of their daily maintenance calories – so half of what they need to hold their weight – for several months. And then they watched what happened.
The results were startling but fascinating. Throughout the study, the subjects continued to lose weight until they simply had nothing else to lose. However, their metabolism never reversed and they never started to gain weight.
Again, this went on for months—much longer than anyone should ever practice intermittent fasting for fat loss. Still, though, that mythic “starvation mode” never reared its ugly head. (2)
Even more modern (and reasonable) studies on fasting have never found starvation mode to be a reality. (3) Interestingly, the metabolism of fasters may decrease slightly but it’s never enough to cause weight gain or create any noticeable negative effects.
Why Intermittent Fasting?
So we’ve established that the 5 meals a day thing doesn’t do all that it promises. But why is intermittent fasting any better?
As we’ve seen, your diet doesn’t actually impact your RMR enough to make a difference, so how can intermittent fasting do anything?
Put simply, intermittent fasting stimulates several hormonal adjustments that change the way your body uses the nutrients it already has. First, your insulin levels drop significantly – hitting a valley at around 24-hours after fasting.
Insulin, an anabolic hormone, tells your cells and body tissue that it’s time to store nutrients that are floating around in your blood. This means that protein, carbs and—you guessed it!—fat all get packed away.
While this is a vital step in maintaining your health, chronically elevated levels of insulin have been linked to a host of health conditions including type 2 diabetes and obesity–along with all the complications they bring with them. Gaining control over your insulin levels, then, is a key step in improving both your overall health and your body composition.
As your insulin levels are plummeting, another hormone is on the rise. Glucagon, a catabolic hormone that opposes insulin, spikes. This lets your body know that, instead of storing things like fat, it’s time to burn them for fuel. Increased levels of glucagon, then, mean that your body will start to do away with some of its stores of fat.
This is exactly what we want.
But wait, I can hear you thinking: “catabolic hormones are bad! They destroy muscle! And I like my muscles!”
And you’re totally correct. Catabolic hormones do break down tissues but only after prolonged starvation. Furthermore, they don’t just destroy muscle; they also go after fat.
Also bear in mind that your body likes your muscles too, so it will wait until the situation is absolutely dire before turning on them. Don’t worry about losing your muscles.
What’s more, the levels of glucagon kicking around in your system are time-dependent, meaning that they continue to rise the longer you fast, taking a steep upturn after about the 48-hour mark. Remember, though, that the benefits of fasting kick in way before that, so you’ll be breaking your fast before your muscles are in any real danger.
Finally, fasting also causes a significant rise in levels of a powerful anabolic hormone (somewhat predictably) called Human Growth Hormone or HGH. (4)
As you fast, HGH runs out to not only build new muscle fibers, but also to protect the ones you already have. So, if you’re still afraid of that mean ol’ glucagon, HGH is on the case.
In reality, these hormonal changes your body goes through during fasting are incredibly similar to those that happen while you’re exercising at high intensity. Now, this doesn’t make intermittent fasting a substitute for activity, but it does show that fasting can complement all of your other healthy living pursuits. All of this with just one daily fast per week!
Right, so fasting is awesome. But how do we do it? More specifically, how do we do it without totally losing our minds?
After all, I will be the first to admit: Eating is fantastic.
This brings us neatly to something that is both a benefit and a necessary step to developing a fasting routine: You need to change your relationship with food.
Fasting will give you an opportunity (read: force you) to take a step back and objectively think about why you eat when you do. Are you really hungry? Or are you just stressed, bored or sad? Honestly answer these questions while you’re fasting and pay attention to what makes you want food.
But that’s sort of an abstract step. Let’s get down to practicalities. Honestly, fasting really isn’t that difficult if you use your time wisely and do it correctly.
Now, there are tons of different protocols and schedules that people use when fasting but let’s just take a simple, 18-hour fast as an example. The key to this, and other schedules, is to remember that the time you spend sleeping counts. Well, unless you unconsciously eat while sleepwalking, but that’s an entirely different topic.
For everyone else, that means that you can easily clock 8-hours of fasting without even trying. If you go to sleep at 10pm, then, and wake up at 6am you already have a pretty respectable head-start. Continue to fast throughout the day—drinking plenty of water—and have your first meal at 4pm.
Congratulations! You made it 18 hours!
Of course, you could start small, and work your way up to these larger fasts but 18 hours is the point at which those benefits really start to kick in.
The Missing 20
At this point, I do feel the need to backtrack a little.
You might have noticed I stated that 70 percent of your caloric expenditure comes from your RMR. We then covered the fact that the thermic effect of food only adds 10 percent. I’m not very good at math but even I know that that doesn’t make 100 percent.
So, what about the other 20 percent? Where’d it go?
Your daily activity.
Naturally, you burn more calories the more you move or workout. Over time, the amount of muscle you carry on your body has a respectable impact on the amount of calories that you burn because your muscle is the foundation of your resting metabolic rate. This is why strength training to build and activate your muscle is so important when it comes to getting rid of body fat and keeping your metabolism healthy.
It also ties in well with everything we now know about intermittent fasting for fat loss. Remember, fasting not only increases the amount of fat that you burn for fuel, it also increases levels of HGH, a hormone that is vital for the growth and maintenance of muscle.
Strength training and intermittent fasting, then, work extremely well in helping you achieve your goals and build the body you want. Intermittent fasting for fat loss is a lot easier than you think it is, and the results are more than worth it.
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Yuri Elkaim is one of the world’s most trusted health and fitness experts. A former pro soccer player turned NYT bestselling author of The All-Day Energy Diet and The All-Day Fat Burning Diet, his clear, science-backed advice has transformed the lives of more than 500,000 men and women and he’s on a mission to help 100 million people by 2040. Read his inspiring story, “From Soccer to Bed to No Hair on My Head” that started it all.