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The Definitive Guide to Why Low-Carb Dieting Sucks

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The Definitive Guide to Why Low-Carb Dieting Sucks

The low-carb diet is the latest fad to take America by storm. And like most fad diets, it has a pretty sales pitch but can’t deliver the goods. Here’s why.


A decade ago dietary fat was the vilest of macronutrients but these days it’s the carbohydrate.


















If we’re to believe the doomsayers, eating carbohydrates produces lots of nasty insulin, which in turn triggers rapid fat storage of damn near anything we eat. The key to health, vitality, and leanness, they say, is to eat as few carbohydrates as possible.

Well, they’re wrong. Unless you’ve overweight and completely sedentary, low-carb dieting sucks, and I’m going to explain why.

You Don’t Lose Fat Faster on a Low-Carb Diet

That statement is basically blasphemous these days, but the general advice of going on a low-carb diet to maximize fat loss is scientifically bankrupt.

There are about 20 studies that low-carb proponents bandy about as definitive proof of the superiority of low-carb dieting for weight loss. This, this, and this are common examples. If you simply read the abstracts of these studies, low-carb dieting definitely seems more effective, and this type of glib “research” is what most low-carbers base their beliefs on.

But there’s a big problem with many of these studies, and it has to do with protein intake.

The problem is the low-carb diets in these studies invariably contained more protein than the low-fat diets.  Yes, one for one…without fail.

What we’re actually looking at in these studies is a high-protein, low-carb diet vs. low-protein, higher-carb diet, and the former wins every time. But we can’t ignore the high-protein part and say it’s more effective because of the low-carb element.

In fact, better designed and executed studies prove the opposite: that when protein intake is high, low-carb dieting offers no especial weight loss benefits. But we’ll get to that in a minute.

Why is protein intake so important, exactly? Because adequate protein intake while dieting for fat loss is vital for preserving lean mass, both with sedentary people and especially with athletes.

If you don’t eat enough protein when dieting to lose weight, you can lose quite a bit of muscle, and this in turn hampers your weight loss in several ways:

1. It causes your basal metabolic rate to drop.

2. It reduces the amount of calories you burn in your workouts.

3. It impairs the metabolism of glucose and lipids.

As you can see, when you want to lose fat, your number one goal to preserve lean mass.

Now, let’s turn our attention back to the “low-carb dieting is better” studies mentioned earlier.

In many cases, the high-carb groups were given less protein than even the RDI of 0.8 grams per kg of body weight, which is just woefully inadequate for weight loss purposes. Research has shown that even double and triple those (RDI) levels of protein intake isn’t enough to fully prevent the loss of lean mass while restricting calories for fat loss.

So, what happens in terms of weight loss when you keep protein intake high and compare high and low levels of carbohydrate intake? Is there even any research available to show us?


There are four studies I know of that meet these criteria and gee whiz look at that…when protein intake is high and matched among low-carb and high-carb dieters, there is no significant difference in weight loss.

The bottom line is so long as you maintain a proper calorie deficit and keep your protein intake high, you’re going to maximize fat loss while preserving as much lean mass as possible. Going low-carb as well won’t help you lose more weight.

It’s Easier to Overeat on a Low-Carb Diet

For many people, the absolute worst part of dieting to lose weight is the hunger pangs, which also often leads to (or amplifies) cravings. There’s truth in the old saying that the best diet is the one you can stick to–compliance is at least half the battle.










Well, a low-carb diet basically guarantees that you’re going to struggle with hunger. 

You see, carbohydrates (and especially the fiber-rich types) have a significant impact on satiety (fullness), whereas dietary fats don’t. That is, eat a bunch of fibrous carbohydrates and you’ll feel very full for quite some time. Eat a bunch of dietary fat and you won’t. (Protein is also very satiating, which is yet another reason why we should eat a lot of it.)

This is especially troubling because dietary fat is so damn tasty and energy dense. It contains about 9 calories per gram compared to the carbohydrate’s 4 calories. This is why research has shown that it’s easier to overeat on a high-fat diet and that obesity is greater among high-fat dieters than low-fat.

My experience working with thousands of people of all ages and circumstances is right in line with the above research: low-carb dieters almost always have more hunger issues than high-carb dieters and struggle more with controlling calorie intake. They also usually have problems with low energy levels as well (which is also not surprising as research has shown very low-carb diets increase fatigue and perceived effort during exercise).

You Build Less Muscle on a Low-Carb Diet

Most people on a low-carb diet are doing so for weight loss purposes, but some try to make it a general lifestyle.

While there’s really nothing wrong with this if you’re sedentary (in fact I would probably argue that it’s a good idea, but that’s another article), if you engage in regular resistance training, a low-carb diet is actually counterproductive because you’ll build less muscle.

Here’s how this works:

When you reduce your carbohydrate intake, you reduce the amount of glycogen stored in the muscles. This, in turn, compromises your performance in the gym–you can expect a dramatic reduction in both muscle endurance and strength, which then limits the amount of progressive overload you can subject your muscles to in those workouts. (And less progressive overload in workouts = less muscle growth over time.)

There are other downsides to low muscle glycogen levels.

Research conducted by scientists at Ball State University found that when muscle glycogen levels are low, post-workout signaling related to muscle growth is impaired. This, by the way, is especially unwanted when you’re dieting for weight loss because a calorie restriction alone already impairs your body’s ability to synthesize proteins.

In athletes, a low-carb diet has been shown to increase cortisol and reduce testosterone levels. This too is particularly problematic when you’re restricting calories, which also reduces anabolic hormone levels.

So, we already know that a low-carb diet won’t help us lose fat faster, but as you now see, it’s looking pretty damn ugly for us weightlifters looking to get lean. It looks like all a low-carb diet does is make our workouts suck and speed up muscle loss.

This isn’t just theory, either.

study conducted by researchers at the University of Rhode Island looked at how low- and high-carbohydrate intakes affected exercise-induced muscle damage, strength recovery, and whole body protein metabolism after a strenuous workout.

The result was the subjects on the low-carbohydrate diet (which wasn’t all that low, actually—about 226 grams per day, versus 353 grams per day for the high-carbohydrate group) lost more strength, recovered slower, and showed lower levels of protein synthesis.

In this study, researchers at McMaster University compared high- and low-carbohydrate dieting with subjects performing daily leg workouts. They found that those on the low-carbohydrate diet experienced higher rates of protein breakdown and lower rates of protein synthesis, resulting in less overall muscle growth than their higher-carbohydrate counterparts.

All this is why I never drop my carbohydrate intake lower than about .8 grams per pound of body weight when cutting (and yes I get to 6% body fat eating this many carbs per day), and I’ll go as high as 2 to 2.5 grams per pound when bulking.

A Low-Carb Diet Impairs Athletic Performance, Too

As intense physical activity pulls heavily on glycogen stores and maintaining optimal performance requires the replenishment of that glycogen, this section shouldn’t really come as a big surprise.

Nevertheless, low-carb “gurus” will often claim that a low-carb diet actually improves athletic performance, usually with a nice little cherry-picked list of studies, so let’s take a closer look at this.

First, it’s worth noting that low-carb dieting has failed to gain any real foothold in the world of professional sports. This industry pays some of the best sports scientists in the world exorbitant amounts of money to figure out how to push the human body to its absolute performance limits, and the low-carb diet hasn’t failed because nobody has thought of trying it–it has failed because it absolutely sucks for athletic performance.

But that’s just an observation. Let’s look at some science.

This study, which is cited almost without fail when trying to sell you the low-carb performance myth, found that when cyclists switched to a ketogenic diet, they first experienced the “keto crash” as the body adjusted to the lack of carbohydrates. This lasted about ten days, at which point the body come “fat adapted” and energy levels improve. Then, for the next four weeks, researchers claimed, there was no decrease in endurance when the cyclists were test at 62-64% VO2max.

What low-carb fanatics don’t tell you (or don’t know themselves), however, is that the head researcher of the study later admitted the cyclists’ ability to perform higher intensity activity (sprinting) deteriorated on the low-carb diet. Not only that, while researchers claimed endurance at 62-64% VO2max wasn’t impaired by the low-carb diet, it was in two of the cyclists, who experienced dramatic decreases in their time to exhaustion (48 and 51 minutes).

Oh and these reductions in performance were not because the cyclists just weren’t “fat adapted” enough. By the end of the study, the cyclists’ respiratory quotient was .72, which is about as fat adapted as you’re going to ever get.

So what this precious low-carb study actually shows us is that a very low-carb (ketogenic) diet is useless for competitive cyclists…and in fact useless for any sport that involves periods of low-intensity and high-intensity activity…or just about every popular sport in the world.

As I noted earlier in this section, this would come as no surprise to professional sports nutritionists. There’s over 50 years of scientific research on the relationship between intramuscular glycogen stores and performance, and the following quote from this extensive review conducted by researchers at the University of Copenhagen summarizes the matter nicely:

“Evidence is presented that short term adaptation, < 6 days, to a fat-rich diet is detrimental to exercise performance.

“When adaptation to a fat-rich diet was performed over longer periods, studies where performance was tested at moderate intensity, 60 to 80% of maximal oxygen uptake, demonstrate either no difference or an attenuated performance after consumption of a fat-rich compared with a carbohydrate-rich diet.

“When performance was measured at high intensity after a longer period of adaptation, it was at best maintained, but in most cases attenuated, compared with consuming a carbohydrate-rich diet.

“Furthermore, evidence is presented that adaptation to a fat-rich diet leads to an increased capacity of the fat oxidative system and an enhancement of the fat supply and subsequently the amount of fat oxidised during exercise.

“However, in most cases muscle glycogen storage is compromised, and although muscle glycogen breakdown is diminished to a certain extent, this is probably part of the explanation for the lack of performance enhancement after adaptation to a fat-rich diet.”

The bottom line is if you want to perform your best in just about any sport you’d actually want to play, you want to eat as many carbs as possible.

Is a Low-Carb Diet Good for Anything, Then?

While I think I make a pretty convincing argument as to why a low-carb diet is terrible for us fitness folk, I do believe there are three valid uses for low-carb dieting:

If you’re prepping for a show or photo shoot or some such thing and want to look as lean as possible.

Following a low-carb diet for 7 to 10 days will reduce the amount of subcutaneous water in your body, which makes you look leaner. Part of getting that “shrink wrap” look is holding as little subcutaneous water as possible (which is why fitness models and bodybuilders often abuse diuretic drugs, which I don’t recommend).

You would then follow this low-carb period with 1 to 2 days of high levels of carbohydrate intake to fill up your muscles with glycogen as you’ll be looking pretty flat without it.

If you’re completely sedentary.

Carbohydrates are primarily energetic–their purpose is to give our cells energy. If you don’t do anything with your body, it doesn’t need very much energy.

Thus, a relatively low-carb diet would make sense for a sedentary person (somewhere around 100 grams per day would probably be plenty).

If you have problems with your insulin response or sensitivity.

Insulin sensitivity refers to how responsive your cells are to insulin’s signals, and insulin response–or insulin secretion–refers to how much insulin is secreted into your blood in response to food eaten.

Research has shown that weight loss efforts aren’t improved or impaired by insulin sensitivity or insulin resistance per se, but there’s evidence that people with poor insulin sensitivity and response may lose more weight on a low-carb diet.

For instance, a study conducted by the Tufts-New England Medical Center found that a low-glycemic load diet helped overweight adults with high insulin secretion lose more weight, but not overweight adults with low insulin secretion.

study conducted by the University of Colorado demonstrated that obese women that were insulin sensitive lost significantly more weight on a high-carb, low-fat diet than a low-carb, high-fat diet (average weight loss of 13.5% vs. 6.8% of body weight, respectively); and those that were insulin resistant lost significantly more weight on a low-carb, high-fat diet than a high-carb, low-fat diet (average weight loss of 13.4% vs. 8.5% of body weight, respectively).

Two studies is hardly definitive, but it’s interesting and worth noting.

Practically speaking, this wouldn’t apply to you unless you’re obese, sedentary, and near diabetic, and don’t want to exercise to lose weight. 

If you’re only slightly overweight and exercise regularly, however, it’s very unlikely that you’re going to have big enough problems with insulin response or sensitivity for the above research to apply to you. You’ll be much better served by a moderately high intake of carbohydrate.


What do you think of low-carb dieting? Have anything else to share? Let me know in the comments below!

I'm Mike and I'm the creator of Muscle for Life and Legion Athletics, and I believe that EVERYONE can achieve the body of their dreams.

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