Carbs and insulin DO matter for weight gain

White sugar with spoon on blue background.

The debates wage on. Do carbohydrates and elevated insulin levels contribute to weight gain and metabolic disease?

We recently posted about an unpublished study from NIH researcher Kevin Hall, PhD that some claimed refuted the carbohydrate insulin model for obesity. But as we mentioned in our post, a two-week study is far too short to adequately measure any meaningful outcomes.

Now, Harvard physician and researcher Dr. David Ludwig and colleagues published a follow up study to his 2018 paper on the carbohydrate-insulin model of obesity.

His original, five-month study showed that those following a diet that sourced just 20% of energy from carbohydrates burned over 200 calories more per day than those following a diet that sourced 60% of energy from carbohydrates.

This was a significant finding to support the concept that carbohydrates and insulin play a crucial role in energy requirements and weight management.

Some questioned the validity of the study results. Dr. Ludwig responded to many of those concerns in a 2020 analysis as well as a 2020 review.

However, his study measured energy output by using a technique called “doubly labeled water.” Some, including Dr. Hall, questioned if that was an accurate way of assessing energy output.

To address this question, Dr. Ludwig and colleagues published their latest paper focusing on dietary energy requirement rather than the doubly labeled water technique, and also compared the results of those who completed the study to all who enrolled, whether they completed the study or not.

They found nearly the same results as the original study with the 20% carbohydrate group expending more energy at rest than the 60% carbohydrate group. Depending on the models used, the extra energy expenditure ranged from 181 to 323 calories per day.

These findings suggest that the doubly labeled water was, indeed, an accurate assessment of calorie output. This validates the original findings and further lends support to the carbohydrate-insulin model for obesity.

Does it prove that this is the one and only contributing factor to obesity?

No, says Dr. Ludwig:

Versions of the carbohydrate-insulin model have been debated for more than a century. No one study could possibly provide a definitive answer on such a complicated topic as obesity.” He points out that many studies, with different approaches, will be needed. “We should focus on studies that will move us closer to an answer, and that requires trials long enough to allow for metabolic adaptation to lower carbohydrate intake.

Another potentially important concept is determining which diet provides the most sustainable energy availability. In another analysis of their dataset, Dr. Ludwig and colleagues published their findings that lower carbohydrate diets had lower insulin to glucagon ratios and better long term energy availability than those eating the higher carbohydrate diet.

Since energy availability may drive feelings of hunger, this may be an important factor in weight loss as well.

The bottom line is that weight maintenance is a complex process that involves many different modulating factors. And based on Dr. Ludwig’s studies, it seems reasonable to conclude that carbs and insulin play an important role for many people, and that this concept deserves continued attention.

We look forward to reviewing more clinically useful studies on this topic as the science evolves.

Thanks for reading,
Bret Scher, MD FACC


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