Q&A: Dr. David Katz of Yale University’s Prevention Research Center

Dr. David Katz at the podium. Photo by Emily Phares.

Heading to the Whole Grains: Breaking Barriers conference this past November, I was excited to listen to a lecture on the grain-shunning Paleo diet. This was, after all, a “whole grains” conference funded by the Whole Grains Council. With swag bags full of granola, cereal, and oatmeal I had a feeling caveman claims would be unwelcome. Fortunately Dr. David Katz, the founding director of Yale University’s Prevention Research Center, was there to address the Stone Age suppositions. I spoke with Katz to find out the truth behind the Paleo diet trend.

What did a true Paleo diet look like, and how is the current Paleo diet different from that?

We can’t remember what we had for breakfast last Tuesday; how accurately do we know what people had for breakfast 50,000 years ago? We know they ate real food direct from nature. And while there’s argument about whether or not our Stone Age ancestors ate mostly plants, the animal flesh they ate was different from modern beef, for example.

There are insights from the Paleo diet about how we ought to eat, but one of the important principles is that our intake of fiber was around 100 grams a day—vastly higher than today. Maybe that’s the important thing about the Paleo diet as opposed to the argument that they didn’t eat grains so we shouldn’t eat grains. I’ve seen nothing in the scientific literature to show that excluding whole grains is an important feature of the Paleo diet.

The Paleo diet excludes whole grains, legumes, and dairy. Conventional wisdom says omitting entire food groups is bad, but some studies of the Paleo diet do show positive effects: its impact on glucose tolerance in people with ischemic heart disease; cardiovascular risk factors in type 2 diabetes; and metabolic syndrome. The sample sizes are small and the studies aren’t long in duration, but what do you make of the positive findings?

When studies show benefit in the short term there are a few things going on. First, the typical American diet is such utter crap that comparing it to anything makes anything look good. Second, the studies that show short-term benefit may have no long-term relevance. If you were obese and you used cocaine for six months, your cardiometabolic profile would improve. Does that mean cocaine would be a good idea for a lifetime? Hardly. You have a short term effect on metabolic markers that can drown out the important influence on lifelong health. Third, do I think [Paleo] is a healthy diet? It probably is, actually. Is it the best diet? I have absolutely no idea. We’ve never had the trials to say let’s see if people can live a hundred years on that diet versus an optimal Mediterranean versus an optimal vegan to see who does the best. We have no real-world evidence that people living on such a diet do well. In contrast, populations that we know of that live the longest and the best, called the Blue Zones, all eat diets of mostly plants which include the things that Paleo diets exclude.

You’ve said that we could eliminate 80 percent of all heart disease, 90 percent of diabetes, and 60 percent of cancer with what we currently know about food, but it seems that every decade there’s a new “healthy” way to eat. One day we are told to eat low-fat and the next it is low-carb. How can we sort through the madness?

The experts who recommended low-fat diets never said eat Snackwell’s cookies. What they were arguing for was plant-based diets. Look at the Okinawans; they have a very low-fat diet and they outlived the rest of us. Everything we ever heard about a low-fat diet was absolutely true. There were two things wrong. First, it’s not the only way to be healthy because the Cretans don’t have a low-fat diet and they outlived the rest of us, too. Second, we kept eating almost the same amount of fat, but diluted down fat as a percent of calories by eating more calories. Big Food turned sensible messages about diet and health into absolute nonsense, invented low-fat junk food, and the public played along.

You’ve said, “What we know about the fundamentals of healthful eating is as decisive as it is dull.” Meanwhile, we keep searching for the perfect diet. What’s the answer to the big “what should we be eating” question?

The “what” is easy. Michael Pollan nailed it. Eat food, not too much, mostly plants. Even if we have doubts about whether a mostly plant diet is better than a more mixed diet or a Paleo style diet, it’s moot because there are 7 billion of us on the planet. We cannot be 7 billion hunter gatherers. The land cost and environmental cost of eating animals, the ethical cost of raising animals, everything argues in favor of a mostly plant based diet.

We used to think fat was the big dietary villain but nutrition science is increasingly pointing the finger at refined carbohydrates. If you read the labels of whole grain products, however, they often look just as processed as white bread products. How are people supposed to identify authentic “whole” grains?

The tendency to focus on macronutrients is obsolete, which leads to problems with labeling. If you are focused on an ingredient or a nutrient, you eat junk but put a halo over it by saying it’s low-fat, low-carb, or gluten-free, or whatever the fixation du jour is. We shouldn’t believe that just because something claims to have whole grain in it, that that makes it virtuous. It’s highly processed junk with essence of whole grain. You need to look for simple, minimally processed foods made with recognizable ingredients. It’s unfortunate that marketers make it hard. In the case of eating well, you need to know what it means, and how to do it.