Is a Low-Carb Diet Safe For Obese Adolescents?

High-protein, low-carbohydrate diets are safe and effective for severely obese adolescent, according to University of Colorado researchers.

Childhood obesity in the U.S. tripled from the early 1980s to 2000, ending with a 17% obesity rate.  Overweight and obesity together describe 32% of U.S. children.  Some experts believe this generation of kids will be the first in U.S. history to suffer a decline in life expectancy, related to obesity.

Colorado researchers wondered if a low-carb, high-protein diet is a reasonable treatment option.  Why high protein?  It’s an effort to preserve lean body mass (e.g., muscle). 

ResearchBlogging.orgThey randomized 46 adoloscents (age 12–18) to either a high-protein, low-carb diet (HPLC diet) or a calorie-restricted low-fat diet to be followed for 13 weeks.  HPLC dieters could eat unlimited calories as long as they attempted to keep carb consumption to 20 g/day or less.  Low-fat dieters were to choose lean protein sources, aiming daily for 2 to 2.5 grams of protein per kilogram of ideal body weight.  Study participants underwent blood analysis and body compositon analysis by dual x-ray absorptiometry.  These kids weighed an average of 108 kg (238 lb) and average body mass index was 39. 

Analysis of food diaries showed the following:

  • Average caloric intake was 1300-1450/day, toward the lower end for the HPLC dieters
  • Energy composition of the HPLC diet: 32% from protien, 11% from carb, 57% from fat
  • Energy compositon of the LF diet: 21% from protein, 51% from carb, 29% from fat
  • Average daily carb consumption for the HPLCers ended up closer to 40 g (still very low) 


Both groups lost weight, with the HPLC dieters trending to greater weight loss, but not to a statistically significant degree.  They did, however, show a greater drop in body mass index Z-score, however.  Study authors didn’t bother to explain “body mass index Z-scores,” assuming I would know what that meant.  Average weight in the HPLC group dropped 13 kg (29 lb) compared to 7 kg (15 lb) in the low-fat group.

Total and LDL cholesterol fell in both groups, and insulin resistance improved.  Neither diet had much effect on HDL cholesterol.

As usual, triglycerides fell dramatically in the HPLC dieters.

Nearly 40% of the kids—about the same number in both groups—dropped out before finishing the 13 weeks.

The HPLC group did not see any particular preservation of lean body mass, and actually seemed to lose a bit more than the low-fat group.

There were no serious adverse effects in either group. 

Surprisingly, satiety and hunger scores were the same in both groups.  [Low-carb, ketogenic diets have a reputation for satiation and hunger suppression.]

My Comments

This is a small short-term study with a large drop-out rate; we must consider it a pilot study.  That’s why I’m not as enthusiastic about it as the researchers.  Nevertheless, it does indeed suggest that high-protein, low-carb diets are indeed safe and effective in obese adolescents.  It’s a start.   

Steve Parker, M.D.

Reference: Krebs, N., Gao, D., Gralla, J., Collins, J., & Johnson, S. (2010). Efficacy and Safety of a High Protein, Low Carbohydrate Diet for Weight Loss in Severely Obese Adolescents The Journal of Pediatrics, 157 (2), 252-258 DOI: 10.1016/j.jpeds.2010.02.010


Filed under Carbohydrate, Fat in Diet, ketogenic diet, Protein, Weight Loss

19 responses to “Is a Low-Carb Diet Safe For Obese Adolescents?

  1. Interesting study. I wonder if they used “Intention to Treat” and included all the subjects in the statistics at the end … that tends to make the studies regress to the mean for both groups (I did a blog post on it at Low Carb Age. I didn’t see a mention of it in the text of the full study you provided.

    On their methodology, I think its a mistake to force an increase in activity level, especially the “30 minutes of vigorous physical activity daily” that increases hunger signals. My 50 pound loss over the past year and a half is due to a LCHP diet, combined with no planned increase in exercise level. Unlike past attempts at losing weight, I never get hungry now. I’m starting on an exercise program now that I’m closer to my goal weight, but will be avoiding “aerobic” style exercise that stimulates hunger for me.

  2. Frank, good point on that “intention to treat” issue. I didn’t see in the article how they handled it. I’d like to think they discarded the data on all the early drop-outs in both groups.

    I agree that vigorous exercise is not very important for weight loss, if at all. The best I can say is that they tried to impose it equally on both groups.

  3. Body mass z-score? Never heard it used that way. I thought z-score was a way of assessing the distribution of a population. Perhaps they’re implying a higher percentage reached that goal of 5% or 10% of body weight loss?

    The elephant in the room is the dropout rate under controlled conditions which seems comparable to other studies. At these rates, we’ll never address obesity from a population standpoint.

  4. And regarding exercise, I’d agree it’s not critical for losing weight but is it not almost a requirement to prevent regaining the weight? Once that metabolism slows down to accomodate for the reduction in calories, it’s all over once the calorie restriction ends in the absence of exercise to prevent the decrease. Say hello to yo-yo dieting.

  5. Isaac you could be right re:diet and exercise after you lose the weight. But in my experience, the “yo yo” effect comes from a temporary diet that you do until you reach goal, and then you go back to eating “normally”.

    People respond to different diets differently. It may be genetic), as some people lose much more than average on a low fat or a low carb diet. And some people lose much more. When you average them out, both diets lose about the same amount for the group overall, but there are outliers. Those that lose nothing on low fat may lose a lot on low carb, and vice versa (the study I linked tested for genetic markers for fat or carb tolerance, and then assigned people to the diet based on that, with much greater success).

    A better approach is to focus on a lifestyle diet change that you adopt for life, not for the “next ten pounds”. Dr. Parker has a point on a Med diet tailored for your health; it is satisfying, fairly easy to follow, and can be a lifestyle choice rather than a temporary “weight loss diet”.

  6. Steve

    Hang on, I have found personally that vigorous exercise does not increase appetite – and have read that this is not uncommon.

    Vigorous exercise I think might have secondary effects. When I have been active I have felt my self-esteem go up – it’s great to feel on top of the world(!) – and that has a carryover effect to making it easier to being disciplined for the rest of the day 🙂

  7. Steve, my wife is the same way; exercise curbs her appetite. But for me, and many others, aerobic exercise triggers hunger. Some people say that weight lifting or other brief periods of exercise are better than 30 minutes of cardio.

  8. lessofmimi

    Studies always frustrate me. Except the ones I do myself. Those have led to huge improvements for my family, too. I’ve got my 10-year old, 4-year old, and my husband all doing a 50-100 gram carb Primal plan for eating and activity (I’m at sub-20 gram carbs for the same plan since I’m T2) and it’s totally healthy, safe, effective, and best of all SHE loves it! For dinner tonight I made zuccghetti – zucchini noodles, mushrooms, diced tomatoes, and organic chicken sausage from our local butcher). We talked about how the comparison between all of the various pastas on the market and zucchini noodles might make an interesting class project. We are all a lot more active now that I’ve lost over 80 pounds, too. I would tend to agree that, in my experience, resistance exercise doesn’t seem to trigger rebound hunger like cardio. If I do a mix of the two (such as swimming) I’m ok, but cardio alone makes me ravenous. But, there’s so much else that plays into that – insulin levels, muscle mass, pre-workout fuel, or not. etc. We are all different (to some extent), but at least for my family, low-carb is the way to go. 🙂

  9. I’m the exact opposite with appetite. Cardio is pretty much neutral on my appetite. But when I do weight lifting or some high intensity interval training where it hits anaerobic, I get ravenous.

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