Should PTs Advocate for a Low Carb Animal Diet or a High Carb Plant Based Diet?

For the last several decades low carb advocates have pitched their diet as means to weight loss, better glycemic control, and even life extension. Many avid fans, like Noakes and Attia, have thrown around several low level studies or short term studies to support the low carb dietary pattern. Meanwhile, the data for more plant focused, carb rich diets like the Mediterranean and Whole food plant based diets have been gleaning more and more support. From prospective trials to population and epidemiology data, such plant focused diets seem to be the ideal pattern for physical therapists (PTs) to recommend to many clients. Let's take a look a recent National Institute of Health (NIH) trial comparing a low carb animal based diet to a high carb plant focused diet.

Published in Nature Medicine, the NIH trial was relatively small and focused on short term results. Researchers housed the participants in a NIH controlled facility, proving to increase the internal validity and controls of the study. Of the 20 participants, half received a low carb, animal-based diet, while the other half received a high carb, plant-based diet. After 2 weeks on one diet, each subject then switched to the other diet. Here's what the macros look like for the study:

Low carb, animal based
- Carbs 10%
- Fat 75.8%
- Protein ~14%
High carb, plant-based
- Carbs 75.2%
- Fat 10.3%
- Protein ~14%

Note that both diets of each group pegged protein intake at the same relative calorie amount, with the obvious factor that the plant-based diet had plant-sources of protein, not meat or animal products. Having equal protein across each diet is important to help control for any protein-related interactions or suggestions of glycemic impact.

The obvious macro difference was the carb and fat amounts, with the low carb diet being very high in fat. As such, those following the high carb, plant-based diet consumed roughly 550-700 calories less each day. Such a calorie deficit translated into significant short term weight loss for those on the plant-based diet. The low-carb group did not gain or lose weight. No surprise here: calories vs calories out!

Glycemic control appeared to be better controlled on the low carb diet compared to the plant-based diet. It is important to understand the subjects were allowed to eat as much of whatever they wanted, whether it was oranges or chickpeas, as long as it fit the macro breakdown for each day. I think this factor may have contributed to slightly higher blood glucose in those on the plant-based diet. It is important to note the slightly higher blood glucose was not "diabetic" and the findings are, again, short-term.

It would be great to see what happens on a more long-term diet. I think with the added calorie deficit of the plant based diet, glycemic control would slowly improve to match that of the low carb diet over time. More interesting would be to examine a third diet: a low-carb plant based diet. It would be fascinating to see if such a diet would produce short term weight loss with good glycemic control. Lastly, this study should highlight to Doctors of Physical Therapy that macro breakdown may not be the sole factor for weight loss. We know that people eating highly processed foods, regardless of macros, tend to gain weight. In the end, people eat food, not macros!

What are your thoughts? How do you think this will impact your PT practice? Let us know on our Facebook page!

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