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Carbohydrates and low-carb diets: what the doctors say
Carbs, keto and low-carb diets: what McDougall, Campbell, Barnard, Ornish and other doctors say, where they agree and differ, with sources.
Updated . For education only, not medical advice.
Our view
The doctors on this site do not treat carbohydrate as one thing: they set whole plant foods such as starches, beans and fruit apart from refined sugar and white flour12. On the refined kind there is little argument even with the low-carb camp, as Alan Goldhamer noted in 2026 and as Dean Ornish has conceded to Atkins followers for decades34.
Low-carb and keto diets do bring weight down at first, and these doctors explain it through fewer calories, a hunger drive muted by ketosis, and in one trial a loss that was mostly not fat567. Their worry is the long run: LDL that climbs, poorer blood flow to the heart, and in a UK Biobank analysis Neal Barnard cited in 2023, roughly twice the rate of heart attack, stroke and artery disease8910.
On the carbohydrate-insulin argument of Robert Atkins and Gary Taubes, that carbs drive insulin and fat gain, we give most weight to the low-fat clinicians: T. Colin Campbell says that case rests on refined sugar, while Peter Rogers and Barnard point to fat as what blunts insulin’s action111213. Walter Kempner reported in 1958 that diabetic patients on a rice diet with over 90% of calories from carbohydrate ended up needing less insulin, the reverse of what he had expected14. Whole populations that lived on starch, from China before 1980 to the Tarahumara of Mexico, are the other evidence they offer1516.
Where they agree
They agree that refined carbohydrate is the problem, not the starch in whole foods: Caldwell Esselstyn’s 2014 heart paper based the diet on grains and legumes while excluding refined carbs, sugars and syrups17. Rip Esselstyn’s PLANTSTRONG site calls unprocessed carbohydrate the body’s main fuel, and Rogers describes starch as sugar packed in fiber that the gut releases gradually1819.
They also agree that low-carb diets can take pounds off in the short term while costing health later; Barnard, Goldhamer and the PLANTSTRONG site all make that trade-off their main objection102021. John McDougall says a large body of research ties high-fat, plant-poor eating of the Atkins type to heart disease, diabetes and cancer, and Campbell said in 2023 that months on such diets set people on course for heart disease2223.
Many see the new versions as the same diet relabeled: Campbell traced the line from Atkins’s 1973 book through South Beach, the Zone and paleo, and Rogers grouped paleo, keto, carnivore and low-carb together in 20262425. McDougall adds that tacking nuts, avocado or soy imitation meats onto a meat and dairy plate does not make it healthy26. On side effects, McDougall and Barnard both name constipation, and Barnard adds an acetone odor and rising cholesterol2728.
Where they differ
Beyond rejecting keto, the doctors differ on how far carbohydrate should go, whether rises in blood sugar after a meal matter, what really drives insulin resistance, why low-carb diets work at first, and how to read the studies2930123132.
How much of the diet should be carbohydrate
The starch doctors go very high: Kempner’s rice diet ran above 90% of calories from carbohydrate, and Jeff Novick held up the Tarahumara diet at about 75 to 80%1416. In 1982 Nathan Pritikin argued that this kind of diet gives the most endurance, citing six athletes he sponsored who took the top four places at that year’s Ironman in Kona33. Walter Willett, by contrast, said in 2020 that the split between fat and carbohydrate matters far less than food quality, and he described diets near 80% carbohydrate in poor countries as built on the cheapest, increasingly refined foods2934. Hana Kahleova made a related point in 2017 about the PURE study: its highest carbohydrate eaters were mostly poor, and soda was counted alongside sweet potatoes35. Campbell, for his part, said that diets with only 15 to 20% carbohydrate are better named high-protein, high-fat36.
Blood sugar after meals
McDougall told viewers in 2022 that raising blood sugar is the point of eating, since the brain and red cells run on glucose, and that rice, corn and potatoes should lift it more than meat does3037. Rogers puts more weight on the difference between starch, which he says releases glucose slowly, and fiber-free sugars, which he says cause a spike and a crash19. For anyone whose triglycerides run high, Esselstyn’s FAQ trims simple carbohydrates such as juice, dried fruit and large helpings of fruit38. Doug Lisle accepted in 2023 that removing refined carbohydrate can steady blood sugar, but said a baked potato does that as well as keto39.
What drives insulin resistance
Rogers holds that fat in the diet is what interferes with the insulin receptor, and Barnard said in 2023 that fat building up inside cells feeds insulin resistance1213. McDougall frames it differently, as the body’s defense against piling on more fat once someone is overweight, and noted that fewer than 1% of people in China had type 2 diabetes before 1980, when white rice was most of the food supply, against 12% now4015. In 2000 Novick wrote that many guests convinced insulin resistance ruled out carbohydrate did well on a starch-based program once other habits changed too41. Jeff Nelson pointed in 2026 to a Barnard trial that randomized people with type 2 diabetes to a low-fat vegan diet or a standard diabetes diet, in which the vegan group lost more weight at 22 weeks and more of them reduced medication42.
Why low-carb diets take weight off
Barnard said in 2017 that cutting carbohydrate removes most of a typical person’s calories, and Campbell said in 2021 that people eat less once they leave a diet of refined carbs543. Lisle described ketosis as a state our ancestors reached mainly when ill and not eating, one that dulls appetite, so weight loss on keto is no surprise to him316. Goldhamer compared high-protein, high-fat diets to a partial fast that blunts hunger for a while20. Kahleova cited a trial in 2020 where keto beat a low-fat plant diet on the scale but lost little fat, and in 2025 described two year-long trials with similar weight loss in which mood scores came out better on the high-carbohydrate diet744.
Reading the low-carb evidence
McDougall wrote in March 2016 that a 2004 keto trial was paid for by the Atkins Foundation, and that its so-called low-fat diet still drew 29% of calories from fat32. Ornish has made two other points: in 2008 he counted only two published studies that measured heart blood flow on an Atkins diet, both showing it worse, and in 2014 he said low-carb studies follow risk factors, while studies that imaged arteries saw blockages grow945. Nelson questioned in 2026 the story that Americans swapped fat for carbs and grew fatter, noting that the supply of sugar topped out near 1999 and declined in the years when obesity went on rising, and he concluded no single nutrient explains it4647.
What each expert says
JMJohn McDougall
McDougall has opposed low-carb eating since the early 1970s, and in a 2024 video he recalled Atkins agreeing with him on the radio that most followers became constipated2227. He tells people that a rise in blood sugar after rice or potatoes is normal and wanted, and he sees type 2 diabetes as a result of excess body fat3740.
Esselstyn’s heart program rests on whole grains and legumes and rules out refined carbohydrates, sugars and syrups17. For high triglycerides his FAQ adds limits on alcohol, white flour, dried fruit, juice and large amounts of fruit38.
Campbell sees every low-carb diet since Atkins’s 1973 book as one idea under new names, and in 2019 he called keto one of the biggest scams in nutrition history2448. In 2021 he argued that keto authors blur carbohydrate from whole plants, which comes with fiber, protein and minerals, with refined sugar111.
Barnard grants that low-carb diets cause weight loss, but in 2017 he cited a small Duke study of 12 people whose LDL rose by an average of 18 points over six months58. In 2023 he pointed to a UK Biobank comparison of just over 300 low-carb, high-fat eaters with about 1,200 other people, in which the low-carb group had about double the heart attack, stroke and artery disease risk10.
Ornish has debated low-carb advocates since Atkins, agreeing that refined carbs are harmful while rejecting the message that bacon and red meat are good for you4. He argues that the arteries, not risk factors, are the real test, and that studies measuring them on low-carb diets found worse results459.
Goldhamer said in 2026 that nearly everyone, keto and paleo advocates included, now agrees refined carbohydrates and processed foods do harm3. In 2024 he said high-protein, high-fat diets may curb hunger and allow short-term weight loss but are a poor strategy over years or decades20.
In 2026 Rogers dismissed paleo, keto, carnivore and low-carb diets, saying his patients who eat mostly starch end up healthy2549. He explains that starch’s fiber slows the release of its glucose and blames dietary fat, not carbohydrate, for insulin resistance1912.
Novick backs a high-carbohydrate diet only when it is built on unrefined plant foods, and in 2007 he contrasted it with the refined, high-sugar American diet that can also be high in carbs2. Reviewing paleo in 2012, he welcomed its stand against processed food but noted that people have eaten starches for at least 30,000 years50.
Nelson argued in 2026 that no single nutrient explains rising obesity, pointing to a sugar supply that fell after 1999 while obesity went on climbing47. Of a cardiologist who blamed carbs and went keto, he said she offered no proof that potatoes, beans or grains had caused her insulin resistance51.
A 2023 post on Rip Esselstyn’s PLANTSTRONG site says keto, paleo, Atkins and South Beach owe their popularity to quick weight loss that comes at a cost to health21. The same post quotes his book on unprocessed carbohydrate as the body’s primary fuel18.
Willett judges carbohydrate by quality rather than amount, and said in 2020 that the fat versus carbohydrate split matters little next to it29. He also warned that diets near 80% carbohydrate, more and more of it refined, are often a sign of poverty34.
Pritikin believed natural, carbohydrate-rich food gave athletes more stamina than any other diet, and in 1982 he cited six athletes he had sponsored at the Kona Ironman, who finished first through fourth in a field of about 85033.
Kahleova rejects the claim that carbohydrates cause disease, and in 2017 she read the PURE study’s high-carb results as a marker of poverty35. She has cautioned against keto for weight loss and, in 2020, during pregnancy, citing research on birth defects752.
Lisle calls keto a weight loss trick that relies on ketosis, an unusual emergency state in which hunger fades316. In 2023 he said a baked potato steadies blood sugar as well as a ketogenic diet does39.
Kempner made carbohydrate the main fuel of his rice diet on purpose, and in 1975 gave its sparing effect on protein and on sodium loss as reasons53. In 1958 he reported that diabetic patients eating over 90% of calories as carbohydrate needed less insulin, not more14.
We follow these doctors in building meals on whole carbohydrate foods such as starches, beans, vegetables and fruit, and in leaving out refined sugar and flour172218. If you have diabetes, take medicines that lower blood sugar, or are pregnant, talk with your own doctor before changing how much carbohydrate you eat. This page is education, not medical advice.
Each small number links to its reference below: the video at the exact second, or the page where it was said.