Barnard and Fung: Opposing Diets for Type 2 Diabetes

Ketogenic and vegan diets clash over type 2 diabetes

A man starts phase two of his keto diet and shares the result plainly: eight kilos lost in twenty-five days. Another boasts of losing twenty kilos in six months eating paleo "like a beast," without hunger. Neither resembles the patient an endocrinologist would send on a carb-heavy insulin regimen. Yet both believe they are right. The question that opens this debate is simple to ask but devilish to answer: how can a high-fat diet and a high-carb diet both claim to control or reverse type 2 diabetes?

Two theories that cannot both be true

Dr. Neal Barnard argues that what prevents sugar from entering the cell is fat accumulated inside it. Hence his prescription: a plant-based diet, low in fat—including vegetable oils—and high in complex carbohydrates, with whole grains, fruits, vegetables, and legumes, minimizing added sugar.

Dr. Jason Fung defends the exact opposite. His thesis is that the cell is not fatty, but "drunk on sugar." He cuts carbs to the minimum, raises fats to maintain satiety, and adds intermittent fasting: fewer carbs, lower blood glucose, less insulin, and, over time, better sensitivity. Both things cannot be true. Or can they? That is where it all begins.

Why opposing diets lower the same blood sugar

Part of the disagreement dissolves when looking closely at the numbers. A gram of carbohydrate from an eggplant does not behave like one from a pastry. According to the breakdown circulating in the conversation, eggplant has about 10% carbohydrates, bread goes up to 60%, and sugar reaches 99%. Removing water from dehydrated fruit multiplies the percentage nearly tenfold. The conclusion many draw: the problem is not the carb, but its concentration.

Hence both schools end up reducing the actual glycemic load, one via fat reduction and the other via whole plants. Fiber is the factor almost no one disputes: a high-fiber vegetable barely spikes insulin. And a potato cooked one day and eaten the next, it is claimed, loses much of its glycemic index.

The common ground: fructose and refined foods

There is a thesis that cuts across the middle of the conflict: the enemy is not carbohydrates as a block, but free fructose and refined products—salt, sugar, and flour. Whoever controls those controls the disease, regardless of which side of the pendulum the diet sits on. Under that logic, both routes would be valid, differing only in the metabolic price they charge.

With that framework, the debate splits into three camps. One group argues that all carbohydrates turn into glucose and that vegetable oils are "the evil." Another calls for moderation without giving up any macronutrient. A third summarizes it with the most repeated phrase of the style: eat everything without obsessing and lead a balanced life.

Testimonials weigh more than studies

Faced with trials and universities, the conversation quickly fills with personal cases. A participant with more than twenty years of type 1 diabetes summarizes his recipe: carbs near zero, strength training, and perfect control. He adds that a doctor proposing heavy carbs "has no clue." Someone compares it to putting out a fire with gasoline.

Not everyone sees it that way. It is warned that proposing fasting to a diabetic or someone with advanced obesity is a direct path to abandonment, and that those who quit return to square one. And some recall that permanent ketosis may be suboptimal: the most likely ancestral pattern was seasonal alternation, not a fixed state.

From insulin to human evolution

As the topic matures, the focus shifts from the plate to the species. There is discussion on when humans appeared—around 150,000 years ago—when fire was domesticated—from 700,000 to 1.5 million years ago—and whether we have carnivore dentition. They cite the canines of our vegetarian relatives, spears from half a million years ago, and the habit of other animals using tools.

Towards the end, the focus turns to agriculture and agrochemicals. Some argue that modern vegetables do not resemble those from two hundred years ago and that pesticides are systemic poisons; others respond that the dose makes the poison and that plants also produce their own chemical defenses.

With the matter thus, the most disorienting figure does not come from a lab: someone recalls that the body can store about 6,000 calories as sugar and does not need external carbs to live. Diabetes, they say, is not decided between two factions: it is decided at every meal.