Below is an approximation of this video’s audio content. To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video.

Whenever I’m asked at a lecture whether some food is healthy or not, my reply is: “Compared to what?” For example, are eggs healthy? Compared to some breakfast sausage next to it? Yes, but compared to oatmeal? Not even close. Think of it as having $2,000 in your daily calorie bank. How do you want to spend it? For the same number of calories, you can eat one Big Mac, 50 strawberries, or a half a wheelbarrow-full of salad greens. Now, they don’t exactly fill the same culinary niche—I mean, if you want a burger, you want a burger—and I don’t expect quarts of strawberries to make it onto the Dollar Menu anytime soon. But, it’s an illustration of how mountainous a nutrition bang you can get for the same caloric buck.

Every time we put something in our mouth, it’s a lost opportunity to put something even healthier in our mouth. So, what are the best foods to eat and the best foods to avoid? Here’s how I like to think of it.

This is my traffic light system to help quickly identify some of the healthiest options. Green means go, yellow means caution, and red means stop (and think before you put it into your mouth).

Ideally, on a day-to-day basis, green category foods should be maximized, yellow foods minimized, and red category foods avoided. As far as I can figure, the best available balance of evidence suggests the healthiest diet is one that maximizes the intake of fruits, vegetables, legumes (which are beans, split peas, chickpeas, and lentils), whole grains, nuts and seeds, mushrooms, herbs, and spices. Basically, real food that grows out of the ground—these are our healthiest choices. In general, the more whole plant foods and the fewer processed and animal foods, the better. So, more green light foods and less yellow and red. Like running red lights in the real world: you may be able to get away with it once in a while, but I wouldn’t recommend making a habit out of it.

My traffic light model stresses two important concepts: Plant foods tend to be healthier than animal foods (in terms of being packed with protective nutrients and fewer disease-promoting factors), and unprocessed foods tend to be healthier than processed foods. Is that always true? No. Am I saying that all plant foods are better than all animal foods? No. In fact, the worst thing on store shelves has been partially hydrogenated vegetable shortening—it’s even got vegetable right in the name! Even some unprocessed plants—such as blue-green algae—can be toxic. Anyone who’s ever had a bad case of poison ivy knows plants don’t always like to be messed with. In general, though, choose plant foods over animal foods, and unprocessed over processed.

What do I mean by processed? The classic example is the milling of grains from whole wheat—for example, to white flour. Isn’t it ironic that these are then called “refined” grains, a word that means improved, or made more elegant? The elegance was not felt by the millions who died from beriberi in the 19th century, a vitamin B-deficiency disease that resulted from polishing rice from brown to white. White rice is now enriched with vitamins to compensate for the “refinement.” A Nobel Prize was awarded for the discovery of the cause of beriberi and its cure—rice bran, the brown part of rice. Beriberi can cause damage to the heart muscle, resulting in sudden death from heart failure. Surely, such a thing could never happen in modern times. I mean, an epidemic of heart disease that could be prevented and cured with a change in diet? Check out my videos on heart disease.

Sometimes, though, processing can make foods healthier. For example, tomato appears to be the one common juice that may actually be healthier than the whole fruit. The processing of tomato products boosts the availability of the antioxidant red pigment by as much as five-fold. Similarly, the removal of fat from cacao beans to make cocoa powder improves the nutritional profile, since cocoa butter is one of the rare saturated plant fats (along with coconut and palm kernel oils) that may raise cholesterol.

So, for the purposes of the traffic light model, I like to think of “unprocessed” as nothing bad added, nothing good taken away. So, in the above example, tomato juice could be thought of as relatively unprocessed, since even much of the fiber is retained—unless salt is added, which would make it a processed food, in my book, and bump it out of the green zone. Similarly, I would consider chocolate processed (since they add sugar), but cocoa powder not.

The limited role I see for yellow-light foods in a healthy diet is to promote the consumption of green-light foods. They can be the spoonful of sugar that makes the medicine go down. So, if the only way I can get a patient to eat oatmeal in the morning is to make it creamy with almond milk, then tell them to add almond milk. The same could be said for red-light foods. If the only way you’re going to eat a big salad is to sprinkle it with Bac-Os, then sprinkle away.

Bac-Os are what are referred to ultra-processed foods—bearing no redeeming nutritional qualities or resemblance to anything that grew out of the ground, and often with added badness. Bac-Os, for example, have added trans fats, salt, sugar, and even Red #40, a food dye that may cause thousands of thyroid cancers every year. As a red light food, it should ideally be avoided, but if the alternative to your big spinach salad with Bac-Os is KFC, then it’s better to sprinkle. The same goes for real bacon bits.

I realize some people have religious or ethical objections to even trivial amounts of animal products. (Growing up Jewish next to the largest pig factory west of the Mississippi, I can relate to both sentiments.) But from a human health standpoint, when it comes to animal products and processed foods, it’s the overall diet that matters. For example, without hot sauce, my intake of dark green leafy vegetables would plummet. Yeah, I could try making my own from scratch, but for the time being, the green ends justify the red means.

On the same note, it’s really the day-to-day stuff that matters most. It really shouldn’t matter what we eat on special occasions. Feel free to put edible bacon-flavored candles on your birthday cake (I’m not actually making those up). Though I guess from a food-safety point of view, a raw cake-batter Salmonella infection could leave you in dire straits. In general, it’s really your regular routine that determines your long-term health. Our body has a remarkable ability to recover from sporadic insults, as long as we’re not habitually poking it with a fork.

That’s why, from a medical standpoint, I don’t like the terms vegetarian and vegan, because they are only defined by what you don’t eat. When I taught at Cornell, I had vegan students who appeared to be living off of French fries and beer. Vegan, perhaps, but not terribly health-promoting. That’s why I prefer the term whole food plant-based nutrition. In general, the dividing line between health-promoting and disease-promoting foods may be less plant- versus animal-sourced foods, and more whole plant foods versus most everything else.

Please consider volunteering to help out on the site.