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What about low-carb diets?

Important Facts About Going Low-Carb

"I want to lose weight, so I cut all the carbs out of my diet!" How many times have we heard this? It's clear that carb-conscious diets such as Atkins and South Beach can produce weight loss, but why?

There are two reasons. First, low-carb diets generally contain fewer total calories than most people eat when not dieting. Second, they produce quick loss of excess body fluid in the first few weeks. Weight loss effects can continue for up to 6 months after initiating low-carb eating.

People feel successful when they lose weight on a low-carb diet, but their heart health is sacrificed in the process (more on that later). Another important point is that after 1 year, the differences between low-carbohydrate and reduced-calorie diets generally are no longer significant (more on that later as well).

So What Constitutes Low-Carb?

A low-carbohydrate diet is one in which fewer than 35% of calories come from carbohydrate. The American Dietetic Association recommends that carbohydrates constitute 45% to 65% of a person's daily diet. Carbohydrates provide an important resource for the body: energy. This energy is used in exercise as glycogen in our blood, liver and muscle.

The American Dietetic Association has published evidence summaries on a variety of diet topics. Three evidence summaries were used to produce this month's column. Each summary reviewed studies on low-carbohydrate diets and produced a grade for dietitians to consider when recommending (or not recommending) a particular diet. The evidence summaries on low-carbohydrate diets rated these as fair or conditional, noting that more research is needed.

What Does Research Show?

When researchers have compared low-carb diets with carb-smart diets of equal calories, they found that both diets in general result in lower calorie intake; thus weight loss ensues.

Among these studies, a randomized, controlled trial followed 68 overweight or obese patients.1 One group followed a diet limited to 30% carbohydrate and the other followed a low-fat, high-protein diet. The research team documented no difference in weight loss outcomes.

Another randomized study assigned 60 participants to a low-carbohydrate diet or an isocaloric diet of 1,300 calories for women or 1,600 calories for men.2 The latter regimen followed the philosophy of the National Cholesterol Education Program, which is often called a modified low-carbohydrate diet. The researchers noted greater weight loss in the low-carbohydrate group - a difference of 6.1 pounds (7.5 lbs vs. 13.6 lbs). Actual calorie intake was not recorded in this study.

Perhaps the most compelling evidence showing the weak scientific support for low-carbohydrate diets is in the studies that look at low-carbohydrate vs. calorie restriction over 6 months and at 1 year. Six studies followed patients dieting on a low-carbohydrate or low-fat regimen.3-8 The results showed that low-carbohydrate diets produced greater weight loss after 6 months. But after 1 year, there was no change in weight loss. These studies did not follow participants long term to determine if weight was regained. There was no difference between the two groups after 1 year of following either a low-carbohydrate or a calorie restricted diet.

Special Populations

What about adolescent obesity and low-carbohydrate diets? Research is limited for this population. One of the few published studies divided patients between a low-carbohydrate diet and a calorie-restricted diet.9 After 12 weeks, adolescent patients who followed a low-carbohydrate diet reported an overall increase in calories consumed on a daily basis (i.e., energy consumed). This study also showed an improved body mass index overall. The low-carb dieters lost more weight than the low-calorie dieters (20.5 lbs to 21.8 lbs vs. 9 lbs to 10.8 lbs).

In addition to children, populations that should avoid low-carbohydrate diets are those with osteoporosis and kidney disease. Patients with these conditions may not be as easily able to reduce calories from carbohydrates as they can total calories or fat calories. Patients with  increased low-density lipoprotein levels are subject to increase saturated and trans fats in low-carbohydrate diets, which worsen cardiac profile and potentially raise harmful cholesterol levels.  

What Should You Recommend?

Evidence analyzed by the American Dietetic Association suggests that although some studies report short-term weight loss and improved BMI with low-carb diets, there is not enough evidence to support long-term use of them. This is particularly true for low-carbohydrate diets that do not restrict calories.

In general, you should recommend a diet that contains 45% to 65% carbohydrates. Most patients process information more successfully without the use of percentages. So, here's a simpler rundown. In a 2,000-calorie diet, 45% of carbohydrate is equal to 900 calories or 225 grams per day. In a 2,000 calorie diet of 65% carbohydrate, intake is equal to 1,300 calories or 325 grams. A 50% carbohydrate intake would be 1,000 calories or 250 grams.

Some evidence suggests that low-carbohydrate diets have untoward effects on blood sugar status.10 One study found that patients on a low-carbohydrate diet had a significant decrease in circulating insulin concentrations, which may result in higher blood sugar.10

What I generally recommend to patients earnestly attempting weight loss with a low-carb diet is to limit use to 3 months. After that, counsel the patient about incorporating a more complete range of foods. Most people will not follow a fad diet for more than 3 months, thus a short-term goal can be established and perhaps met. Being open to the discussion paves the way for further healthful goals and maintenance of a healthy weight for a lifetime.


Robyn Kievit is a family nurse practitioner who is a registered dietitian and a certified specialist in sports dietetics. She operates a private nutrition practice in Boston. E-mail your nutrition and weight loss questions to or visit her website at On Facebook and Twitter, search for nutritionmentor.



1. Luscombe-Marsh ND, et al. Carbohydrate-restricted diets high in either monounsaturated fat or protein are equally effective at promoting fat loss and improving blood lipids. Am J Clin Nutr. 2005;81(4):762-772.

2. Aude YW, et al. The National Cholesterol Education Program diet vs. a diet lower in carbohydrates and higher in protein and monounsaturated fat: a randomized trial. Arch Intern Med. 2004;164(19): 2141-2146.

3. Brehm BJ, et al. A randomized trial comparing a very low carbohydrate diet and a calorie-restricted low fat diet on body weight and cardiovascular risk factors in healthy women. J Clin Endocrinol Metab. 2003;88(4):1617-1623.

4. Brehm BJ, et al. The role of energy expenditure in the differential weight loss in obese women on low-fat and low-carbohydrate diets. J Clin Endocrinol Metab. 2005;90(3):1475-1482.

5. Nickols-Richardson SM, et al. Perceived hunger is lower and weight loss is greater in overweight premenopausal women consuming a low-carbohydrate/high-protein vs. high-carbohydrate/low-fat diet. J Am Diet Assoc. 2005;105(9):1433-1437.

6. Samaha FF, et al. A low-carbohydrate as compared with a low-fat diet in severe obesity. N Engl J Med. 2003;348(21):2074-2081.

7. Yancy WS, et al. A low-carbohydrate, ketogenic diet versus a low-fat diet to treat obesity and hyperlipidemia: a randomized controlled trial. Ann Intern Med. 2004;140(9):769-777.

8. Landers P, et al. Effect of weight loss plans on body composition and diet duration. J Okla State Med Assoc. 2002;95(5):329-331.

9. Sondike SB, et al. Effects of a low-carbohydrate diet on weight loss and cardiovascular risk factor in overweight adolescents. J Pediatr. 2003;142(3):253-258.

10.  Meckling KA, et al. Comparison of a low-fat diet to a low-carbohydrate diet on weight loss, body composition, and risk factors for diabetes and cardiovascular disease in free-living, overweight men and women. J Clin Endocrinol Metab. 2004; 89(6): 2717-2723.

Nutrition Now Archives

I loved this article and agree that patients don't process % or even calorie numbers, but I tell them a rule of them is to eat whole foods, no processed foods, plan meals ahead of time, add vegetables and fresh herbs to dishes for variety and always bring meals with them to work or school so they don't make poor choices with fast foods when they are hungry.

Teri O'Neil,  FNP,  private officeSeptember 30, 2010
Walkersville, MD

For a young teenager ,what's more important than losing weight and if it is done by eating low or no carbs for a quick weight loss than all the luck to you. Don't worry about nutrition. They are young and losing weight is more important and I have seen success on Atkins diet.

sharon wander,  M.D.September 30, 2010
wilkes Barre, PA


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