Low-Carb vs. Low-Fat Weight Loss Diets

The battle has raged (well, there's been disagreement) as to whether a low-carb diet or a low-fat diet produces the best results in obese people trying to lose weight.  Previous studies have suggested that low-carb diets are more likely to produce earlier weight loss than low-fat diets, but results after one year are mixed.  That’s why the findings of a new study, reported in the Annals of Internal Medicine, have attracted attention.   

The study, which was done at three US university medical centers, compared weight loss after two years in obese subjects on a low-carbohydrate or a low-fat diet, with both groups receiving a comprehensive lifestyle modification program.  The study enrolled 307 people with a body mass index (BMI) between 30 and 40 kg/m².  There were 99 men and 208 women with an average age of 45½.  The low-carb group was instructed to eat up to 20 grams of carbs a day for 3 months, and then increase by 5 grams a day each week until they reached their desired weight.  The low-fat group was told to decrease their calorie intake to 1,200 to 1,800 calories a day, with less than 30% coming from fat.  The lifestyle program met weekly for 20 weeks, then alternate weeks for 20 weeks, and then monthly for the rest of the 2-year study.  Weight, blood pressure, cholesterol levels, bone density, and adverse symptoms were collected at 3, 6, 12, and 24 months.

After one year, the subjects had lost an average of 24 pounds (11% of bodyweight), which had fallen to 15½ pounds (7% of body weight) after two years.  There were no differences in weight or bone mineral density between the two groups at any time point.  However, those in the low-carb group had more rapid early declines in diastolic blood pressure (the bottom number), triglyceride levels, and very-low-density cholesterol levels, and greater increases in high-density cholesterol levels (that lasted through the 2 years, averaging +23% at 2 years); their reductions in low-density cholesterol was less than in the low-fat dieters, and they had more adverse symptoms.        

It must be pointed out that people with diabetes or high cholesterol levels were not included in the study, so these results might not apply to them.  And many subjects dropped out of the study before the 2 years was up.  Nobody said that dieting was easy!  But the study shows there are two distinct dietary paths to losing weight, if you’ve got the willpower – and a good lifestyle support program.