Low-carb versus bioenergetics: the evolving debate on human diets

A recent podcast episode features a fierce debate between obesity expert Eric Westman and neuroscientist Jay Feldman over the merits and risks of low-carbohydrate diets, highlighting ongoing disagreements about optimal human nutrition and metabolic health.

A long-running dispute over carbohydrates took centre stage in a recent episode of Ben Greenfield’s podcast, where obesity medicine specialist Eric Westman and neuroscience and exercise physiologist Jay Feldman set out sharply different views on what humans should eat, how metabolism works and whether low-carbohydrate diets help or harm over time.

Westman, who helped build Duke University’s low-carb clinic and has spent decades treating obesity and type 2 diabetes, argued that carbohydrate restriction remains one of the most effective clinical tools for reversing metabolic disease. He said he first became interested in the approach after seeing patients lose substantial weight on what he described as the Atkins diet, and later helped develop low-carbohydrate research at Duke. Feldman, by contrast, said his work is grounded in what he calls a bioenergetic view of health, in which the body’s ability to produce energy efficiently inside cells is central, and he contended that carbohydrate intake supports that process.

Their discussion quickly moved from diet labels to biochemistry. Feldman argued that fat oxidation is less efficient than glucose use because it produces a different balance of electron carriers in mitochondria, potentially increasing oxidative stress and forcing the body into a more stressful hormonal state. He said those changes can show up indirectly in blood markers such as higher glucagon and lower T3, the active thyroid hormone, especially during long-term low-carb eating. Westman pushed back, saying much of that reasoning is still theory unless it is clearly shown in human studies, and argued that blood markers do not necessarily reveal what is happening inside cells.

The two also disagreed on the meaning of ketosis. Westman said humans naturally enter ketosis after a few days without food and suggested that this shows the state is normal rather than pathological. He pointed to work from Isabella Cooper on people adapted to ketogenic diets, and said that when carbohydrates were reintroduced, some markers worsened before returning to baseline after ketones were restored. Feldman countered that short-term changes should not be confused with long-term health effects and compared ketosis to cortisol: a necessary response that can still become problematic when it is prolonged.

A further fault line emerged over evolution and lifespan. Westman argued that humans evolved in conditions where food was often scarce, and said low-carb diets can be therapeutic for diabetes, obesity and other metabolic conditions. Feldman replied that survival in the absence of food is not the same as optimal health, and suggested that starvation pushes metabolism down to conserve energy rather than to promote thriving. He also challenged the idea that a slower metabolic rate automatically means longer life, saying patterns seen across species do not necessarily hold within species because of other biological factors, including differences in mitochondrial membranes. Westman remained sceptical, saying the human evidence still favours using carbohydrate restriction as a practical clinical intervention, particularly for weight loss and insulin resistance.

Greenfield, who largely steered the exchange, closed by noting that exercise, activity levels and practical adherence may matter as much as carbohydrate ratios for many people. He argued that people with very different training loads may need very different diets, and that for many listeners the simplest starting point remains the familiar formula of eating less and moving more before obsessing over macronutrient details. The discussion ended without consensus, but with both guests acknowledging that there is more than one route to better health, even if they disagree profoundly about which one is best.