Quite a few people have asked me to comment on the blog Authority Nutrition. It’s written by Kris Gunnars, a medical student at the University of Iceland.

First, despite the bold title of his blog, Gunnars is no authority on nutrition. His background is the usual one of the self-proclaimed expert: “I got interested in my own health and started reading books and studies on nutrition.”

The result is that his blog is an interesting mix. There is some good advice and thoughtful observation, but also many overstatements of the evidence as well as some overt misinformation.

But he is certainly popular and it’s not hard to see why. He writes with great confidence and he challenges the nutrition status quo. He cites studies, which gives his blog an impression of legitimacy. There is a certain appeal to “authorities” who tell you exactly what to eat and what not to eat, and why everybody else is wrong. If you’re a Paleo dieter who likes this sort of thing, you’ll love Kris.

Gunnars promotes low-carb diets (although he thinks some starchy foods are okay for those with high calorie needs), so it’s no surprise that he doesn’t like vegan diets. Nor does he like the way vegan diets are sometimes promoted or portrayed. Neither do I. Which is why I did in fact agree with some of what he said in his recent post Top 11 Biggest Lies About Vegan Diets.

For example, I agree that some vegans spread unscientific fear-mongering about animal foods, and sometimes overstate benefits of veganism. And yes, it’s possible that many people experience improvements in health when they go vegan because they reduce their consumption of refined grains and processed foods at the same time.

But Gunnars gets things a little confused regarding this point. He says that a properly-planned vegan diet is actually called a “whole foods, plant-based” diet and that it eliminates all processed foods, refined grains, vegetable oils, and refined sugar. He says that any benefits seen with vegan diets are due to the elimination of these components, not to the lack of animal foods.

Here’s the catch, though: The studies that suggest that vegan diets may lower blood cholesterol levels and reduce risk for hypertension, diabetes and heart disease looked at plain old vegans. (1-4) There is no evidence to suggest that they were all avoiding oils, processed foods like veggie meats or refined grains.

And, it’s not true, as Gunnars contends, that vegans were compared to people eating usual “junk food” western diets. The meat-eaters in the EPIC-Oxford study, for example, were more health conscious than the general British population.

Like Gunnars, I doubt that a vegan diet is the one and only healthy way to eat. But his insistence that observed health benefits of vegan diets have nothing to do with avoiding animal foods doesn’t necessarily fit the evidence.

He’s also unimpressed with the lower saturated fat content of vegan diets because, he says with great certainty, the saturated fat “myth” has been debunked.

It’s this type of certainty that suggests more than anything that he doesn’t understand how complex nutrition research is. It’s true that the effects of saturated fat appear to be more nuanced than we once thought. For example, some types of saturated fat may be more harmful than others. And the benefits of reducing saturated fat intake depend very much on what you replace it with.

The hard lesson we’ve learned over the past few decades is that eating more refined carbs in place of saturated fat doesn’t lower heart disease risk; it’s likely to raise it. But replacing saturated fat with polyunsaturated fats does lower heart disease risk.

This relationship is actually reinforced in some of the studies that Gunnars cites as “proof” that you don’t need to worry about saturated fat. (5,6) For example, he says that the Cochrane review of clinical studies on fat found that reducing saturated fat had no effect on heart disease. What the report actually says is that the best advice for anyone at risk of heart disease is to reduce saturated fat and replace it in part with unsaturated fat. Gunnars ignores that advice because he thinks polyunsaturated fats are unhealthy.

To show the nutritional inadequacy of vegan diets, he drags out the same old arguments and half-truths that I’ve addressed before. It is simply not true that “83% of vegans” have a vitamin B12 deficiency. Vegans who take B12 supplements are no more likely to be deficient than meat-eaters and are probably less likely.

And yes, we have lower iron levels. But that’s not necessarily a bad thing. And yes, we need to make sure we get enough vitamin D by getting adequate sun exposure or taking a supplement or using fortified foods. Just like meat eaters do if they aren’t eating sword fish or salmon every single day.

Regardless, the need to supplement with vitamin B12 and possibly DHA is really all that divides us from the carefree life of a meat-eater. Gunnars’ reaction to this is that it makes a vegan diet a “pretty bad idea.” Mine is a shoulder shrug. As always, when you recognize the moral imperative of veganism—and Gunnars admits that he doesn’t—then whatever little tweaks you need to make to your diet to keep it healthy are not that big a deal.

Nobody knows what the single best diet is. The only question that matters is “Can you be healthy on a vegan diet?” And the answer is “yes.” There is nothing in the Authority Nutrition blog that disproves that.

1. Serum concentrations of cholesterol, apolipoprotein A-I and apolipoprotein B in a total of 1694 meat-eaters, fish-eaters, vegetarians and vegans. Bradbury KE, Crowe FL, Appleby PN, Schmidt JA, Travis RC, Key TJ. Eur J Clin Nutr 2014;68:178-83.

2. Hypertension and blood pressure among meat eaters, fish eaters, vegetarians and vegans in EPIC-Oxford. Appleby PN, Davey GK, Key TJ. Public Health Nutr 2002;5:645-54.

3. Type of vegetarian diet, body weight, and prevalence of type 2 diabetes. Tonstad S, Butler T, Yan R, Fraser GE. Diabetes Care 2009;32:791-6.

4. Risk of hospitalization or death from ischemic heart disease among British vegetarians and nonvegetarians: results from the EPIC-Oxford cohort study. Crowe FL, Appleby PN, Travis RC, Key TJ. Am J Clin Nutr 2013;97:597-603.

5. Meta-analysis of prospective cohort studies evaluating the association of saturated fat with cardiovascular disease. Siri-Tarino PW, Sun Q, Hu FB, Krauss RM. Am J Clin Nutr 2010;91:535-46.

6. Reduced or modified dietary fat for preventing cardiovascular disease. Hooper L, Summerbell CD, Thompson R, et al. Cochrane Database Syst Rev 2011:CD002137