Ask almost anyone what they need to do to lose a few pounds, and they'll probably say: "Cut back on carbs." As a nutrition coach, I've heard it hundreds of times.
While the low carb movement has spiked and dipped in popularity since the Atkins surge of the early 2000s and now the Ketogenic diet craze, most people now assume that carbohydrates are inherently fattening.
In the past few years, I’ll bet you’ve heard (or thought) at least one of the following:
Carbs spike your blood sugar and insulin, which slathers on the body fat.
Carbs, especially sugar and grains, cause inflammation.
Carbs are not an essential part of the diet like fat and protein.
Seems simple and logical. Which is the problem.
These simplistic statements about “good foods” and “bad foods” ignore biological complexity and the bigger picture.
Now, do carbs increase insulin levels?
Yes, they do.
Does increased insulin after meals automatically lead to fat gain?
No. (Insulin’s actually a satiety hormone — in other words, it makes you feel full — so the idea that on its own it leads to fat gain doesn’t make sense.)
Are carbs really inflammatory?
That depends. Are we talking about processed corn syrup, a bag of Doritos, or a Hawaiian roll? Probably. But if we’re talking about real whole grains, not really.
Are carbs less important than protein, fat, and the many micronutrients that contribute to our health?
Again, if you’re talking about processed carbs, the answer is a resounding yes. But if you’re talking about whole, minimally processed carbs—like whole grains (when tolerable), potatoes, sweet potatoes, fruit, beans, legumes—that’s a different story.
Can a low-carb diet work to help people lose weight?
Of course it can.
Is it because it is low in carbs?
Maybe. Maybe not.
Can eating an appropriate amount of carbs actually help you look, feel, and perform your best?
You bet it can.
The problem with not eating carbs
As a weight-loss strategy, cutting carbs (while reducing the total number of calories) clearly works pretty well for some people. If it didn’t, then Atkins would have never been popular in the first place.
Here’s the thing, though: Carb reduction costs us.
You see, most of us require some level of carbohydrates to function at our best over the long term.
Sure, we can cut carbs temporarily if we need to lose weight quickly. But for most of us, keeping carbs too low for too long can have disastrous consequences.
This is especially true for those of us who work out.
If you’re sedentary, your carb needs are lower. So you might be able to get away with more restriction.
But if you like to exercise regularly and enthusiastically, restricting your carb intake too drastically can lead to:
decreased thyroid output which can have a severe effect on your metabolism and how your body manages blood glucose
increased cortisol output and decreased testosterone (which is a sure-fire recipe for losing muscle and gaining fat)
impaired mood and cognitive function
suppressed immune function.
In other words: Your metabolism might slow, your stress hormones go up and your muscle-building hormones go down.
You feel lousy, spaced-out, sluggish, cranky… and maybe even sick.
Most surprising of all: You probably don’t even lose that much weight in the long term.
Low carbs are not better for fat loss
The logic seems so clear and appealing: High carbs lead to insulin which leads to fat storage. Low carbs keep insulin low, which should get you effortlessly lean while you enjoy chicken wings, salmon, eggs, and butter.
Indeed, many people who try low-carb dieting are initially pleased by an immediate weight loss… which is mostly water and glycogen. So, in the short term, it seems like low-carb diets are superior.
But does long-term evidence support low-carb dieting?
Research says no. Over the long haul, any differences between low-carb and other diets even out.
Protein: The hidden X-factor
Most studies that suggest low-carb diets are superior suffer from a common methodological flaw: They usually don’t match protein intake between groups. This means that the low carb group often ends up consuming significantly more protein.
We know that getting plenty of protein has many advantages:
protein has a higher thermic effect — our bodies have to “rev up” to digest it (you’ll know this if you’ve ever gotten the “meat sweats” after a big steak);
protein makes people feel fuller, longer; and
protein helps people retain lean mass.
In other words, the big “secret” might be a high protein diet rather than a low carb diet.
So let’s play fair and look at a study where protein was matched. In this study, subjects who ate a moderate carb diet (40% calories from carbs) reported significantly better mood, and lost about the same amount of weight as those on a ketogenic low-carb diet (5% calories from carbs).
Actually, the group who ate a moderate amount of carbs showed a small (though not statistically significant) tendency to lose more body fat as compared to those on a low carb diet (12.2 lbs vs 7.4 lbs in 6 weeks).
Both diets improved insulin sensitivity. However, the ketogenic diet also increased LDL cholesterol and inflammatory markers, and subjects who were on it felt less energetic.
So, in this study:
moderate carb eaters felt better
moderate carb eaters lost about the same amount of weight, maybe even a little more
both types of eaters improved insulin sensitivity
the low carb dieters ended up with worse blood work and inflammation
Makes you wonder why low carb gets so much hype, doesn’t it?
Especially considering that a recent review of long-term low carb versus low fat diets — the largest of its kind so far — found that both low carb and low fat diets reduced people’s weight and improved their metabolic risk factors.
In this review, both diets had about the same weight loss, changes in waist circumference, and measurements of several metabolic risk factors (blood pressure, blood glucose, insulin).
Still, it would be great to understand more about what makes low carb diets “work” at all.
One recent study asked: Do low carb diets work because they restrict carbs or because they tend to increase protein?
Over the course of one year, the researchers compared four different conditions:
normal protein, normal carbohydrate
normal protein, low carbohydrate
high protein, low carbohydrate
high protein, normal carbohydrate.
Interestingly, the two groups eating the high protein lost the most weight.
And the real kicker? Varying the levels of fats and carbs seemed to make no difference to body composition.
What this means for you
1. Strict diets aren’t the answer
If your eating plan isn’t working for you, it’s tempting to make it more restrictive. You might assume that if you aren’t losing fat going kinda low-carb, you should go full ketogenic.
But more restriction almost never works.
Don’t take your nutrition to extremes — unless you have extreme goals.
Strategic moderation, as unsexy as that sounds, is the only sustainable method.
2. Most of us need some carbs
Most of us will look, feel, and perform our best when we balance a reasonable amount of lean protein, quality carbs, and healthy fats.
Precision Nutrition's standard hand-based portion size recommendations aren’t just what I think is best. They’re what I know is best, based on careful research, and they're experience with 20,000 clients to date.
3. Experiment & have fun
These recommendations let you be flexible, enjoy the high-quality foods you love, and adjust your intake to your own experience, goals, and unique needs.
Don’t like rice? Fine. Try another carb source.
Don’t like beef for your lean protein? How about eggs?
Need more carbs to support your athletic performance? Cool. Add another serving and see how it goes.
Need fewer carbs because you know aren't moving as much throughout the day? Cool. Cut your serving in half and see how it does.
Curious about balancing your blood sugar by dialing back the carbs just a little bit? Great — give it a go, monitor your glucose levels, and see how you feel.
YOU are unique. Your body is unique.
Your individual carb requirements depend on your:
goals (fat loss, muscle gain, maintenance)
genetics (different body types, medical conditions)
carb source (refined versus minimally processed)
activity level (sedentary, weight-training, endurance athlete).
4. Keep it simple
Don’t overly restrict; don’t over-think it; don’t waste time with “carb math”.
Enjoy a wide variety of minimally processed, whole and fresh foods.
Observe how you look, feel, and perform.
Decide what to do based on the data you collect about yourself, not on what you think you “should” do. Be your own detective and test it out on yourself.
The only “rules” come from your body and your experience. Don’t follow a dietary prescription for anyone else’s body.
And above all, for most active people, carbs are your friend!