Which Body Type Is Best for the Low Carb Diet?

One Study Compares the High Carb-Low Fat Diet vs. Low Carb-High Fat Diet

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Do low-carb diets work better than high-carb low-fat diets? That's the question many people ask themselves as they rev up for the low carb meal plan. However, that answer isn't so cut and dry. There is no single diet that works best for everyone. I think that a major goal of the next phase of diet research is to figure out which diets will work best for which people. This small, but extremely well-controlled study, published in Obesity Research earlier in 2005, is a great contribution to that effort.

Insulin Resistant vs. Insulin Sensitive

Depending on how your body metabolizes, how you eat can make the scale go up or down. In the aforementioned study, researchers studied people who are were insulin-resistant vs. those who were insulin-sensitive. Their results found participants who were insulin-resistant lost more weight on a reduced carbohydrate diet, whereas people who were insulin-sensitive lost more weight on a high carb/low-fat diet.

Low Carb Diet Works for the Right Person

The researchers hypothesized that people who are insulin resistant might respond better to a diet that is less glycemic (due to fewer ​carbs and more fat) than people who have normal insulin sensitivity. So they took a group of mildly-moderately obese women and put the ones who were most insulin resistant in one group, and the ones who were most insulin sensitive (least resistant) in another. They didn’t use people who were in the middle, to make the results clearer.

Next, they figured out everyone’s metabolic rate, body composition, and how many calories their bodies were using. Then, for 16 weeks, each subject was given food to eat that would be 400 calories less than they needed to maintain their body weight. Half of each group received a diet that was low in fat and high in carbohydrates (60% of the diet), and the other half ate a diet that was higher in fat and lower in carbs (40% of the diet).

Differences Despite Tailor-Made Food Plan

The results were nothing short of astonishing. Despite being on diets where the calorie levels were tailor-made for each individual, the results varied wildly depending both upon diet content and insulin sensitivity level:

  • The insulin resistant people lost 13.4% of their body weight – average almost 25 lbs - on a low-carb diet, but only 8.5% (average 16 lbs) on a high carb/low-fat diet
  • The results for the insulin sensitive folks were precisely the reverse – 13.5% body weight lost (average 25 lb) on the high carb diet and 6.8% (average 13.5 lbs) on the low-carb diet.

Remember: They were all getting a calorie level custom-adjusted to each person, and they were all getting their food from the clinic.

Additional Interesting Results from the Study

  • Fasting insulin levels dropped in all groups, but more in both insulin resistant groups.
  • Insulin sensitivity improved in the insulin-resistant groups, the low-carb more than the high-carb (possibly because more weight was lost).
  • Triglycerides improved in all groups except for the insulin resistant group on the high carb diet. That group increased their triglycerides significantly.
  • The two “mismatched groups” (losing the least amount of weight) lost the amount of weight that would be expected, given their calorie levels. The big mystery still to be solved is why the “matched” groups lost so much more than would have been expected.
  • People did not report changing their activity levels through the study (and had been instructed not to).

Small But Solid Results

Though the study was awfully small (only 21 subjects), in a way that makes it more impressive that the results were so dramatic. Updated research shows their results have held up over the years. Also, it is short-term, and we are all familiar by now with the track record for short-term vs long-term weight loss. Still, it was a carefully done study, and hopefully will be the foundation for many more along these lines.

Cornier MA, Donahoo WT, et al. Insulin sensitivity determines the effectiveness of dietary macronutrient composition on weight loss in obese women. ​Obesity Research Apr 13(4) (2005) 703-9.

Gardner CD1. Tailoring dietary approaches for weight loss. International Journal of Obesity Supplements. 2012 Jul;2(Suppl 1):S11-S15.