Can low-carb diets really help people lose weight? Of course they can. But that doesn't necessarily make them your best choice. In fact, if you exercise regularly, reducing your carb intake too far can be a bad idea. Find out why.
Let's get one thing straight from the start. Low-carb diets can help many people lose weight.
But is this way of eating healthy or sustainable?
My conclusion, based on a thorough review of the science and my experience with thousands of coaching clients at Precision Nutrition, is this:
- If you're a person who's fairly sedentary, you might be able to get away with it. For a while.
- But if you're someone who likes to exercise and who works out regularly, eating a low-carb diet for a significant length of time may hurt you more than it helps.
So why are low-carb diets so popular?
Sometimes, we get so caught up in fad diets that we forget to look at the evidence. But fad diets are mostly bad diets.
For many years, we thought the secret to maintaining our weight was to eat lots of carbs and reduce our fat intake. Just think of the old Food Guide Pyramid with grains at the bottom and oils at the top.
You probably know what happened. Low-fat, high-carb didn't work for most of us. People felt deprived and hungry. They "cheated" with "fat-free," high-sugar treats. And many of us got fatter. To the point where the AMA has labelled obesity as a disease. (I've commented on that here).
Then the pendulum swung, people hopped on the low-carb, high-fat bandwagon, and it was party time with almond butter, bacon, and heavy cream.
Unfortunately, for most of us, low-carb doesn't work so well, either.
What's wrong with restricting carbs?
Reducing your intake of healthy carbs can lead to the following problems:
- a sluggish metabolism
- lower levels of muscle/strength-building hormones
- higher levels of stress hormones.
The result? You might find yourself feeling cranky, tired, weaker, or even sick.
Oh, and your weight loss will probably also stall.
Why does this happen? Let's take a closer look at what the latest research says. (And if you'd like even further proof, check out this article).
Decreased thyroid function.
In order to function properly and to maintain an appropriate metabolism, our body produces an important hormone called T3.
T3 is the most active thyroid hormone and is important for blood glucose management and proper metabolic activity.
Guess what? Studies show that when calorie intake or carb intake is too low, T3 levels drop.
If you're active, you need adequate energy and carb intake for a healthy thyroid.
Cortisol up; testosterone down.
People who exercise regularly need to eat enough carbs or their testosterone will fall while their cortisol levels rise. This is a sure-fire recipe for losing muscle and gaining fat.
Not to mention, feeling generally awful.
Carbohydrates and women's hormones.
We now know that eating too few calories or low-carb for too long can cause significant disruptions to many hormones.
This seems especially true for women, whose bodies may be more sensitive than men's to low energy or carbohydrate availability.
When we think about building muscle, we usually think of protein. But research shows that lowering carb intake can affect your muscle mass even if your protein consumption stays constant.
Yup. You could be guzzling protein shakes or eating steak five times a day. And you'd still be losing muscle if you weren't getting enough carbs!
Which is not to say that you don't need protein.
Protein: The hidden success factor.
Most studies that suggest low-carb diets are superior suffer from a common methodological flaw: They don't match the protein intake between groups. This means that the low-carb group often ends up consuming significantly more protein.
Higher protein diets help to control appetite and have a "thermic" effect, causing our bodies to "rev up" in order to digest. So could protein be the hidden success factor in low carb diets?
Over the course of one year, 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.
Most of us need some carbs.
The moral of this story is that it doesn't make sense to overly restrict any macronutrient. Or to oversimplify your food discussion by classifying foods as either good or bad.
Most of most of us will look, feel, and perform our best when we balance a reasonable amount of lean protein, quality carbs, and healthy fats.
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).
If you're wondering how to determine your needs, click here for some tried and tested portion size recommendations.
And remember to focus on healthy carbs, of course.
Strict diets are not the answer.
If you're eating low carb and have lost a little weight, you might be tempted to keep going that way. You might even decide that if low carb is working, lower carb would be even better. Maybe you want to go full on ketogenic!
But I wouldn't recommend it. Especially if you're an active person.
Remember, carbs are not the enemy. Oversimplification is.
Eat reasonable portions of healthy foods in every category, and do that consistently. Your body will reward you by feeling and performing its best.
Want some help finding the best diet for you? Download this free guide: Paleo, vegan, intermittent fasting... Here's how to choose the best diet for you.
About the author.
John Berardi, Ph.D. is a founder of Precision Nutrition, the world's largest online nutrition coaching company. He also sits on the health and performance advisory boards of Nike, Titleist and Equinox.
Dr. Berardi was recently selected as one of the 20 smartest coaches in the world by livestrong.com, the internet's most popular fitness site.
In the last five years, Dr. Berardi and his team have personally helped over 30,000 people improve their eating, lose weight, and boost their health through their renowned Precision Nutrition Coaching program.
Anderson KE, et al. Diet-hormone interactions: protein/carbohydrate ratio alters reciprocally the plasma levels of testosterone and cortisol and their respective binding globulins in man. Life Sci. 1987 May 4;40(18):1761-8.
Bisschop PH, et al. Isocaloric carbohydrate deprivation induces protein catabolism despite a low T3-syndrome in healthy men. Clin Endocrinol (Oxf). 2001 Jan;54(1):75-80.
Brinkworth GD, et al. Long-term Effects of a Very Low-Carbohydrate Diet and a Low-Fat Diet on Mood and Cognitive Function. Arch Intern Med. 2009;169(20):1873-1880.
Davidson MB, Chopra IJ. Effect of Carbohydrate and Noncarbohydrate Sources of Calories on Plasma 3,5,3-Triiodothyronine Concentrations in Man. J Clin Endo Metab. 1979;48(4).
E Danforth, Jr, et al. Dietary-induced alterations in thyroid hormone metabolism during overnutrition. J Clin Invest. 1979 November; 64(5): 1336-1347.
Gleeson M, Bishop NC. Modification of immune responses to exercise by carbohydrate, glutamine and anti-oxidant supplements. Immunology and Cell Biology. (2000) 78, 554-561
Howarth KR, et al. Effect of glycogen availability on human skeletal muscle protein turnover during exercise and recovery. J App Physiol. 2010;109(2):431-438.
Hu T, et al. Effects of Low-Carbohydrate Diets Versus Low-Fat Diets on Metabolic Risk Factors: A Meta-Analysis of Randomized Controlled Clinical Trials. Am J Epidemiol. 2012 Oct 1;176 Suppl 7:S44-54.
Johnston CS, et al. Ketogenic low-carbohydrate diets have no metabolic advantage over nonketogenic low-carbohydrate diets. Am J Clin Nutr. 2006 May;83(5):1055-61.
Lane AR, Duke JW, Hackney AC. Influence of dietary carbohydrate intake on the free testosterone: cortisol ratio responses to short-term intensive exercise training. Eur J Appl Physiol. 2010 Apr;108(6):1125-31.
Phinney SD, et al. The human metabolic response to chronic ketosis without caloric restriction: preservation of submaximal exercise capability with reduced carbohydrate oxidation. Metabolism. 1983 Aug;32(8):769-76.
Phinney SD. Ketogenic diets and physical performance. Nutr Metab (Lond). 2004 Aug 17;1(1):2.
Serog P, et al. Effects of slimming and composition of diets on V02 and thyroid hormones in healthy subjects. Am J Clin Nutr. 1982;35(1):24-35.
Soenen S, et al. Relatively high-protein or 'low-carb' energy-restricted diets for body weight loss and body weight maintenance? Physiol Behav. 2012 Oct 10;107(3):374-80.
Spaulding SW, et al. Effect of caloric restriction and dietary composition of serum T3 and reverse T3 in man. J Clin Endocrinol Metab. 1976 Jan;42(1):197-200.
Tsai L, et al. Basal concentrations of anabolic and catabolic hormones in relation to endurance exercise after short-term changes in diet. Eur J Appl Physiol Occup Physiol. 1993;66(4):304-8.