The McDougall Diet

Dr. McDougall is a maverick who disagrees with most experts. He recommends a high starch, low fat diet with no dairy or animal foods and other prohibitions. Its severe restrictions make it nutritionally questionable and it has never been properly tested in a controlled study.

It is commonly believed that people who want to lose weight should avoid starchy foods like potatoes and pasta, and low-carb diets are often recommended. I was surprised to hear that a medical doctor, John A. McDougall, was recommending a starch-based diet for weight control. He claimed patients on his diet lost 6-15 pounds a month while eating as much as they wanted of approved foods. He was even claiming that a high-starch diet could be used to treat chronic diseases such as arthritis, cancer, diabetes, osteoporosis, and heart disease.

I found that hard to believe; but since McDougall is an MD board certified in internal medicine, I couldn’t just dismiss him as an uneducated quack. I assumed he must have found convincing evidence to support his claims. I read his book The McDougall Program: 12 Days to Dynamic Health hoping to find that evidence. I was disappointed. The book was full of anecdotes, testimonials, lists of foods that are permitted or prohibited, shopping lists, menus, and high starch recipes. Many claims were made without supporting evidence. Evidence appeared only twice:

  1. In Chapter 3, he says “Scientific support for the material in this chapter” can be found in another of his books, The McDougall Plan, published in 1984.
  2. Part 3 covers dietary and lifestyle treatment of medical conditions and is followed by a section of references applying to the material in Part 3.

The section on Treatment of Medical Conditions included a lot of questionable statements. He says lactose cannot be digested by most adults; that’s simply wrong. Under Diabetes, he claims that patients with childhood-onset diabetes will usually drop their insulin needs by 30 percent and their blood sugar levels will be more stable (less brittle). None of the listed references support that claim. He says insulin dose adjustments should be made “as usual, with the aid of urine sugar and blood sugar tests”. Does anyone still monitor diabetics with urine tests? The references are outdated, all from the 1970s and 1980s. He recommends never taking oral hypoglycemic drugs because they increase your chances of dying sooner. (Wrong! More recent studies have demonstrated that they actually reduce mortality.) And he says he usually stops the pills of adult-onset diabetics the very day they start his Program. That could be dangerous!

He blames diet for hair loss because he read a book review of a Japanese book with the title Can Hair Grow Again? He says treating high blood pressure with medications doesn’t work. Wrong! It demonstrably does. I was particularly intrigued by the discussion of Multiple Sclerosis. He says that for most of his patients with MS, the progress of MS symptoms has been halted. He cites a study by Dr. Roy Swank, saying he treated more than 3,000 MS patients with a low fat diet; he says Swank’s results are unchallenged by other studies and are unmatched in effectiveness. Swank’s study began in 1949 and his results for 144 patients were published in The Lancet in 1990. There was no control group. And his results certainly have been challenged, repeatedly. A recent study reported decreased subjective self-reports of fatigue but “no significant improvement on brain MRI, relapse rate or disability”.

The references listed were far from convincing. For example, there were five references for acne. The most recent one was from 1981; the others dated back to 1964, 1966, 1969, and 1977. More recent articles and systematic reviews with different findings were not listed, such as a 2016 Cochrane review that said “only a small proportion of studies met sufficiently high scientific standards that would enable therapeutic recommendations to be made in practice”.


I scrupulously resisted reading the criticisms of other people until I had given the book a chance. After it failed to convince me, I found that there were plenty of others who were equally unconvinced. My SkepDoc’s Rule is “Before you accept a claim, try to find out who disagrees with it and why.” In this case, pretty much all health care providers and nutrition experts disagree, and they have a very good reason: they follow the published evidence. How likely is it that they are all wrong and this one individual is the only one to get it right? Not very.

McDougall claims there is “overwhelming evidence” to support his diet. An article on SkepticBlog has fun with his claim that dairy food causes all disease:

And the science is overwhelming! Well, if this guy says so, it must be true. But I wonder how he has come to this conclusion, since McDougall has not managed to convince any meaningful percentage of the medical community that outrageous claims are anything other than quackery. This total failure constitutes “overwhelming science”?

That article goes on to point out that the preponderance of published research supports exactly the opposite of what McDougall claims. Nutritionist Kurt Butler agrees, saying that while McDougall backs up his claims with published medical studies, his interpretations of those studies are often at odds with the studies’ authors.

The Wikipedia article on McDougall concludes, “There is no scientific evidence that McDougall’s diet is effective”.

A book review by Stare and Whelan says McDougall has “peculiar ideas about food” and “eccentric ideas about the relationship between food and disease”. It concludes that:

The concepts in this book are extreme and out of keeping with nutrition reality. The diet is nutritionally precarious and, we hope, too austere for anyone to think about trying to follow.

What exactly is the McDougall Program?

  1. Follow a diet centered around starches with the addition of fresh or frozen fruits and vegetables.
  2. Give up meats, fish, poultry, dairy products, eggs, oils, refined foods, alcohol, and caffeine (except for rare special occasions). Limit fat, sugar, and salt.
  3. Exercise every day.

McDougall has long offered an inpatient program in Santa Rosa, California, but now the same program is available to people who stay at home, for a reduced cost of $2,495. Whether inpatient or online, dramatic results are promised: improved appearance, rapid weight loss, lower blood pressure and blood sugar, improved biomarkers for cardiac risk, and an end to annoying discomforts like headaches, bowel irregularity, and chronic fatigue.

Other possible explanations

Patients who experience those improvements will attribute them to the Program, but are all those restrictions really necessary? I suspect not. They might see similar improvements if they reduced total calorie intake by other means and exercised regularly. Suggestion and psychological factors surely play a part. It would be nice to have a controlled study comparing the McDougall diet to a less restrictive, nutritionally balanced, calorie-limited diet. But we don’t; and I doubt if we will in the foreseeable future. Meanwhile, I’d rather accept the preponderance of evidence than the questionable assertions of a maverick. Some of McDougall’s recommendations are in line with mainstream advice, but there is reason to fear that strict adherence to his whole Program might result in nutritional deficits that could do more harm than good.

This article was originally published in the Science-Based Medicine Blog.

Dr. Hall is a contributing editor to both Skeptic magazine and the Skeptical Inquirer. She is a weekly contributor to the Science-Based Medicine Blog and is one of its editors. She has also contributed to Quackwatch and to a number of other respected journals and publications. She is the author of Women Aren’t Supposed to Fly: The Memoirs of a Female Flight Surgeon and co-author of the textbook, Consumer Health: A Guide to Intelligent Decisions.

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