A research study published in Annals of Internal Medicine takes straight on the debate over the efficiency and safety of a low-carbohydrate diet compared to a more conventional low-fat, low-calorie diet.
Other studies evaluating the effectiveness of each diet had found that low-carbohydrate diets resulted in a more significant weight loss at six months than a low-fat, low-calorie diet. Studies done for a two year duration have shown mixed results.
Low-Carbohydrate Versus Low-Fat Diet Study Design
In this study, researchers wanted to “evaluate the effects of long-term (two years) treatment with either a low-carbohydrate or low-fat, calorie-restricted diet,” while monitoring cardiovascular risk factors, bone mineral density, general symptoms, along with body weight and body composition.
The study was conducted in three different locations- Denver, Colorado; St-Louis, Missouri; and Philadelphia, Pennsylvania. Participants had no serious medical conditions, were between the ages of 18 and 65 years old, and had a body mass index (BMI) of 30 to 40 Kg/m2 (obese). Approximately half the participants followed an Atkins-type low-carbohydrate diet while the other half were put on a low-fat diet.
What set this study apart is the inclusion of a comprehensive educational component that included topics such as self-monitoring, stimulus control, and other skill builders for both types of diet.
Diet Study Results
The data collected on a regular basis included weight, blood HDL (good) cholesterol, LDL (bad) cholesterol, and triglycerides; blood pressure, bone mineral density, body composition, and a variety of symptoms from bad breath to constipation.
Here is a synopsis of the results for some of the data collected:
- Body weight: Participants in both groups lost about 11% of their body weight at six months and 12 months, experienced some regain to finish at a 7% weight loss at two years. Researchers found no significant difference in weight loss between the two diet groups.
- Blood lipids: The study revealed that subjects on the low-fat diet experienced a greater reduction in LDL (bad) cholesterol levels at three and six months, but that the difference did not persist at 12 and 24 months. Triglyceride levels dropped further in the low-carbohydrate group at three and six months but not at 12 or 24 months. Lastly, HDL (good) cholesterol levels were significantly higher in the low-carbohydrate group than in the low-fat group throughout the entire duration of the study.
- Bone mineral density and body composition: Researchers found no differences between the two groups in regards to changes in bone mineral density or body composition over two years. Additionally, both groups lost a similar percentage of weight from fat and lean mass.
- Symptoms: A significantly higher number of participants on the low-carbohydrate diet reported symptoms of bad breath, hair loss, dry mouth, and constipation, compared to those on the low-fat diet. However, except for constipation, those symptoms were limited to the first six months.
The most surprising finding that came out of comparing both diets is that neither one distinguished itself as the best way to lose weight on a long term basis. In fact, researchers suggested that the diet micronutrient composition (i.e. fat vs carbohydrate) did not influence weight loss when calorie level was fixed. The calorie level of participants in this study was indeed similar since the lifestyle change interventions provided produced the same calorie reduction in both groups.
In regards to cardiovascular risk factors, the low-fat diet triggered the expected early reduction in LDL cholesterol, while folks on the low-carbohydrate diet experienced an increase; however those outcomes leveled off at two years.
In the end, the only difference between the two diets was the higher HDL cholesterol level among participants on the low-carbohydrate diet. At this point, researchers are not sure why this change occurred and what it means from a cardiovascular risk stand point. Clearly, as with more areas of study, more research is needed to confirm any sort of conclusion.