This study published in JAMA last week confirms what we’ve been saying about the importance of keeping insulin levels low to achieve and maintain weight loss by minimizing the glycemic load in a diet. The study also supports the growing recognition that not all calories are the same.
There are 2 ways to keep the glycemic load low in a meal. One is to focus on the source of the carbohydrate and eat foods that are low-glycemic, that is foods that have minimal effect on blood sugar and insulin levels. The sccond way is to simply restrict intake of all carbohydrates in the meal (very low carbohydrate diet). This study looked at those two diets, plus a third one consisting of consumption a low fat diet. A low fat diet is essentially a high carbohydrate diet.
The study evaluated the effects of these 3 diets on hormone levels, energy expenditure at rest, total energy expenditure, inflammation and metabolic markers.
Here’s what the study found.
Energy Expenditure (Calorie Burning)
The low fat diet (high carbohydrate diet) was associated with fewer total calories burned and fewer calories burned at rest. The very low carbohydrate diet was associated with better total energy expenditure (calories) and at rest. The low-glyemic diet was intermediate with respect to energy expenditure.
Blood pressure improved with each diet compared to baseline and the reduction was similar in all 3 diets. The very low carbohydrate diet produced the greatest improvements in a majority of the metabolic components, however was associated with higher cortisol (stress hormone) levels, and CRP or C-reactive protein, a marker of inflammation was higher with the very low carbohydrate, yet still improved compared to baseline and well within a healthy range.
CRP was decreased in all 3 diets with the low-glycemic index showing the greatest reduction in inflammation. Inflammation is a causative factor in most chronic diseases including obesity.
Thyroid function was lower in the very low carbohydrate diet compared to the other 2 diets. Thyroid regulates metabolism. This is interesting because the very low carbohydrate diet was associated with the best energy expenditure. This means there is another mechanism at play to offset the decline in thyroid function seen with very low carbohydrate diet in order to explain the better energy expenditure.
The low fat diet was associated with lower insulin sensitivity (bad).
Not All Calories are the Same
The take home message with this study is that not all calories are the same. Gary Taubes, in his books Good Calories, Bad Calories and Why We Get Fat has been a driving force behind that concept. The very low carbohydrate and low-glycemic diets stood out in this study compared to the low fat diet.
Though the very low carbohydrate diet showed slightly better outcomes compared to the low-glycemic diet it may have some downside in terms of stress hormones and inflammation. In the long run, the very low carbohydrate may be more challenging to adhere to. Therefore, we still favor the low-glycemic diet overall for most of our patients and readers.