You are leaving Medscape Education
Cancel Continue
Log in to save activities Your saved activities will show here so that you can easily access them whenever you're ready. Log in here CME & Education Log in to keep track of your credits.


Low-Carbohydrate Diets and Adolescent Weight Control: Promising Option or Oxymoron?

  • Authors: Presenters: David L. Katz, MD, MPH, FACPM, FACP, and Dale A. Schoeller, PhD; Moderator: George D. Lundberg, MD
Start Activity

Target Audience and Goal Statement

This activity is intended for physicians and other healthcare professionals who provide primary care to adolescents and their families.

The goal of this activity is to provide physicians and other healthcare professionals with information on the trends in obesity and diabetes among adolescents, the appropriateness of carbohydrate restriction for weight loss, and the hazards of dieting in adolescence.

Upon completion of this activity, participants will be able to:

  1. Describe the recent trends in obesity and diabetes among adults and children in the United States
  2. Assess the differences between a low-carbohydrate diet and a low-fat diet for short-term and long-term weight loss
  3. Recognize the fallacies in the arguments supporting various popular diets, particularly low-carbohydrate diets
  4. Describe the dietary pattern best supported by evidence for both overall health and lasting weight control in adults and children/adolescents


As an organization accredited by the ACCME, Medscape requires authors and editors to disclose any significant financial relationship during the past 12 months with the manufacturer of any product that may relate to the subject matter of the educational activity, whether or not the activity is commercially supported. Authors are also asked to disclose any mention of investigational products or unapproved uses of products regulated by the U.S. Food and Drug Administration.


  • George D. Lundberg, MD

    Editor in Chief, MedGenMed and Editor in Chief, Medscape Core


    Disclosure: Dr. Lundberg has nothing to disclose at this time.

  • David L. Katz, MD, MPH, FACPM, FACP

    Associate Clinical Professor of Public Health & Medicine, Yale University School of Medicine, New Haven, Connecticut


    Disclosure: David L. Katz, MD, MPH, FACPM, FACP, has no significant financial interests or relationships to disclose. Dr. Katz has reported that he does not discuss any investigational or unlabeled uses of commercial products in this activity.

  • Dale A. Schoeller, PhD

    Professor, University of Wisconsin Department of Nutritional Sciences, Madison, Wisconsin


    Disclosure: Dale A. Schoeller, PhD, has no significant financial interests or relationships to disclose. Dr. Schoeller has reported that he does not discuss any investigational or unlabeled uses of commercial products in this activity.

Accreditation Statements

    For Physicians

  • The American College of Preventive Medicine (ACPM) is accredited by the Accreditation Council for Continuing Medical Education (ACCME) to provide continuing medical education for physicians.

    ACPM designates this educational activity for a maximum of 1.0 category 1 credit toward the AMA Physician's Recognition Award. Each physician should claim only those credits that he/she actually spent in the activity.

    Supported in part by project # 5 P02 MC 00064 from the Office of Adolescent Health, Maternal and Child Health Bureau, Health Resources and Services Administration, Department of Health and Human Services.

    Contact This Provider

For questions regarding the content of this activity, contact the accredited provider for this CME/CE activity noted above. For technical assistance, contact [email protected]

Instructions for Participation and Credit

There are no fees for participating in or receiving credit for this online educational activity. For information on applicability and acceptance of continuing education credit for this activity, please consult your professional licensing board.

This activity is designed to be completed within the time designated on the title page; physicians should claim only those credits that reflect the time actually spent in the activity. To successfully earn credit, participants must complete the activity online during the valid credit period that is noted on the title page.

Follow these steps to earn CME/CE credit:

  1. Read the target audience, learning objectives, and author disclosures.
  2. Study the educational content online or printed out.
  3. Online, choose the best answer to each test question. To receive a certificate, you must receive a passing score as designated at the top of the test. Medscape encourages you to complete the Activity Evaluation to provide feedback for future programming.
You may now view or print the certificate from your CME/CE Tracker. You may print the certificate but you cannot alter it. Credits will be tallied in your CME/CE Tracker and archived for 5 years; at any point within this time period you can print out the tally as well as the certificates by accessing "Edit Your Profile" at the top of your Medscape homepage.

The credit that you receive is based on your user profile.


Low-Carbohydrate Diets and Adolescent Weight Control: Promising Option or Oxymoron?: Poll Question


Poll Question

George Lundberg: Which is a poll question, an opportunity for our listeners/viewers/learners to weigh into this thing. The poll question reads, "If there is no metabolic advantage to the low-carbohydrate diet, why is there a greater weight loss than with a low-fat diet?" Answer A, it's the water loss; B, people eat less; C, it's a mystery; D, other, or I don't know.

While the audience is voting, I'll have another question for Dr. Schoeller.

Dr. Schoeller, a listener asks, "If a person insists on going on a low-carb diet, should that person also be taking nutritional supplements at that time?"

Dale Schoeller: Absolutely. As I'll address a little bit later on, one of the disadvantages of the low-carb is that it avoids foods which are high in the B vitamins and high in a number of trace elements. When you remove those foods from the diet, you're likely to be deficient in those nutrients. For good health, they will need a multivitamin.

George Lundberg: OK, very good. Well, we have several dozen people who have voted in the poll, and I'm happy to say that they seem to have learned something. The poll results are: 73% vote "it's the water loss," 26% that "people eat less," and zero voted for "it's still a mystery" or "other" and "I don't know."

So, Dr. Schoeller, proceed with part 2 of your presentation.

  • Dale Schoeller: OK, part 2. I'm going to start to provide more answers to that question, so I'll address it over the next number of slides, but I will say it's not just the water loss. That water loss difference really only continues for the first 1-2 weeks in the diet. Thereafter, the difference in weight loss suggests that something else is going on.

  • (Enlarge Slide)
  • This is just reiteration of our caloric balance equation. The energy that goes in the diet has to equal the energy that goes out in energy expenditure, plus the change in body energy stores. Based on that, we can predict how much weight a person should lose when they go on a diet.

  • (Enlarge Slide)
  • In healthy but overweight individuals who are on a nutrient-sufficient diet, the amount of weight they lose over a period of 6, 12, and 24 weeks averages 80% of fat by weight. We know how many calories there are in a kilogram of fat, so we can look at those rates of weight loss over that dietary period, dietary restriction period, and predict that if a person decreases their energy intake 1,500 calories per day below their expenditure, they should be losing about 3 pounds per week. At the other end of the scale, if they're only decreasing their intake by about 100 calories per day, they'll only be losing about one tenth of a pound per week.

  • (Enlarge Slide)
  • Knowing that, let's look at the results of a couple of published studies of weight loss that I've referred to earlier. One is the outpatient study in adolescents by Sondike, and the other is the inpatient study in which individuals were fed only 1,000 calories per day.

    Shown here in the graph are the rates of weight loss in pounds per week for the 6-week inpatient study and for a 24-week outpatient study. You'll notice that again, the low-carb diet only shows the greater weight loss in the outpatients. This suggests again that it's not just the water loss, and also that the rates of weight loss are slower in the outpatient setting than in the inpatient setting.

    Well, if we're going to conserve energy and obey the laws of thermodynamics, that means that the inpatient study, which was 1,000 calories per day, must not be being met in terms of the intakes in the outpatient study. The outpatients must be eating more than 1,000 calories per day, or else they'd be losing weight more rapidly.

    This suggests that the differences in weight loss in the inpatient and the outpatient study are largely due to how well a person complies with the energy restriction. The differences that we've been talking about between a low-carb diet and a low-fat diet are due not to just the water loss, but are actually due to differences in compliance with the reduced caloric intake strategy of a diet.

  • (Enlarge Slide)
  • So, why is it that patients are a little bit more compliant on a low-carb diet?

  • (Enlarge Slide)
  • We don't know all the answers, but we do have some evidence, again, from the literature. One is that short-term satiety on a high-protein diet is greater. This was a study that was done in 35 preschool children, so we don't have to extrapolate for adults, which also shows similar results, by the way. But in the study, they provided a controlled lunch, following a snack that was either high in protein or high in carbohydrates. The children who consumed the lunch, an ad libitum lunch, following the snack that was high in protein ate less.

    So there's something about these low-carb diets that is good, and it's probably that they're a little bit higher in protein than the average low-fat diet that is prescribed. So if you're going to prescribe a diet, do pay attention to the protein intake.

  • (Enlarge Slide)
  • The other advantage of a low-carb diet is that it restricts the food choices a person has. Many studies have shown that the more variety on the plate in front of you, the more you're likely to eat. Nowhere is this more obvious than in a restaurant setting. If you are on some sort of restricted diet which says I cannot eat food X, Y, and Z, in this case, carbohydrate diets, on that plate in front of you, you're not going to eat the bread, you're not going to eat the dessert, because that's high-carb. You're not going to eat the potatoes along with it. So there are fewer calories on your plate while eating out. Many studies have shown that the people who eat out more, because we're overserved in almost every restaurant we go to, tend to gain more weight.

  • (Enlarge Slide)
  • The other advantage of a low-carb diet, that may help people stay on that diet, is they're often given keto sticks so that they can test their urine daily to detect if they've overconsumed carbohydrate. That's a good form of biofeedback, and it helps a person with a daily compliance to a diet. So, the bottom line here is that these low-carbohydrate diets work because people eat fewer calories.

  • (Enlarge Slide)
  • However, in the 1 long-term study that has been done in adults, that decrease, or that difference, the rapid weight loss that is seen in the first 12-24 weeks, dissipates when you start to look at these people after another 6 months, so there's no difference in weight loss on the typical low-fat diet or a low-carb diet.

  • (Enlarge Slide)
  • Are there any other limitations to the low-carb diet?

  • (Enlarge Slide)
  • Well, there is one that is very important for the adolescent. The low-carb diet suggests somewhere between 20 and 90 g of carbohydrate per day, depending upon which phase you're in. That has been shown in many studies to be insufficient for participation in sports. Physical activity and sports participation is very important to many adolescents. By cutting out the carbs, you're going to be cutting out their ability to perform.

    It's also been known that the incidence of headache, probably due to the dehydration and low blood glucose and lethargy related to the low blood glucose, increases on the low-carb diet.

    Finally, as we answered a little earlier in the talk, the low intake of whole grains and fortified grain products that accompany a low-carb intake provide a diet that's low in B vitamins and many minerals, so that a vitamin and mineral supplement is needed.

    When you get to the bottom of the list, you have to ask yourself, why are we putting adolescents, or for that matter anyone, on this rollercoaster of weight gain -- followed by weight loss, followed by going back to bad dietary habits and regaining weight? We can avoid all of these negative consequences by better instilling a family approach, as Dr. Katz has indicated, which emphasizes good skills for controlling dietary intake and for increasing physical activity.

  • (Enlarge Slide)
  • But let's return to the mystique of the low-carb diet again. As indicated by the published evidence, there are indeed differences in weight loss on a low-carb diet. During that first week, however, they're due only to increased water loss -- no health advantages there at all. The idea of a metabolic advantage on this low-carb diet, so you can eat all you want and still lose weight, is not supported by any evidence of measured energy expenditure. The differences in weight loss at 12 or 24 weeks that have been reported in the literature are due to consuming fewer calories on the low-carb diet.

    So why not just consume fewer calories on a healthy diet? And, finally, the differences that are reported in many of the short-term studies have not been shown to continue when the patients are followed out to a 1-year interval.

  • (Enlarge Slide)