How to Evaluate Which Foods Are Healthy

A realistic guide to making good decisions about what to eat

John Fawkes
Feb 6 · 12 min read
Photo by monkeybusinessimages

If you do a quick Google search for “which foods are healthy and which aren’t,” you’ll get millions of results. Almost all of them will be list articles with titles like these:

50 Foods That Are Super Healthy

6 Best Foods To Boost Your Health

12 Foods You Should Stop Buying — And 17 You Should Eat

The 30 Healthiest Foods To Eat Every Day

These are all real titles from real articles, even the last one that implies you should be eating 30 different foods every day. And if you read these, they all give you the same unhelpful advice:

Eat: Salmon, avocados, walnuts, almonds, chicken breast, eggs, quinoa, berries, cucumbers, apples, carrots, broccoli, milk, olives

Don’t eat: Donuts, pizza, white bread, oil, peanuts, beer, eggs and milk again for some reason

Okay… cool. But why? Most of these articles list a few simple reasons for each. Eggs have cholesterol, but also B vitamins; almonds have healthy fats and protein; broccoli has fiber, and so on.

But all of that begs a bigger question: what are the principles that all of this is based on? What are the criteria for declaring food healthy or unhealthy?

You’ll rarely see anyone take a step back and try to codify the first principles from which these “healthy” and “unhealthy” lists are created, but I’m going to take a crack at that right now.

This list isn’t exhaustive, but for most purposes, it will give you all you need to know to evaluate how healthy any given food is. After reading it, you’ll be able to identify the low-hanging fruit, so to speak, in your diet — the few food swaps you can make to produce the biggest improvement in your health.

Caloric Density

What does caloric density mean? Simply put: calories per unit of weight and/or volume.

Looking at a few items around my apartment right now — the cold cut ham and turkey has 70 calories per 57-gram serving or 1.23 calories per gram. The trail mix has 180 calories per 28-gram serving, or 6.43 calories per gram. So the meat is a clear winner here.

The least calorie-dense foods, though, are vegetables like carrots, broccoli, etc. They have almost no calories, so filling up on them is a great way to eat fewer calories. Zero-calorie beverages are even better from this standpoint — you can’t live off them, but they can help curb your appetite at no caloric cost.

If you’re underweight and/or trying to bulk up, this consideration actually gets reversed, and foods with higher caloric density will be desirable, at least in the 12–18 hour period after you lift weights for 30 minutes or longer. However, highly calorically dense foods tend to also be low in things like protein, fiber, vitamins, and minerals, so even when bulking you shouldn’t completely throw the caloric density principle out the window.


Not all proteins are created equal. Animal proteins are superior to plant proteins across the board, for a few reasons. First, most plant protein sources don’t have complete amino acid profiles — the main exceptions being soybeans, vegan meat substitutes, and vegetable protein mixes such as a soy/rice/pea protein blend.

Second, even if they do have a complete amino acid profile, vegetable protein sources don’t have as much leucine as animal protein sources. Since leucine is the main amino acid responsible for signaling muscle protein synthesis, this means plant proteins will stimulate less muscle protein synthesis.

With that said, the best protein source is protein powder, followed by lean meats and fish, followed by fatty meats, fish and eggs, followed by meat substitutes like tofu or tempeh, then finally high-protein vegetable foods like beans, lentils, and almonds. Anything else shouldn’t be thought of as “a protein source,” even though most foods have some protein.

Dietary Fiber

Soluble fiber gets absorbed into the bloodstream and clears plaque out of your arteries. It mainly benefits cardiovascular health.

Insoluble fiber can’t be absorbed, but it aids digestion of other nutrients, provides fecal bulk so you don’t get diarrhea, and massages the intestines, reducing your risk of intestinal illnesses like colon cancer and inflammatory bowel disease. In other words, it mainly benefits digestive health.

Both types of fiber reduce the risk of cancer and help you live longer. They also are associated with a lower risk of infection and respiratory illness, though it’s not clear if there’s a direct causal relationship there.

In this case, vegetable foods come out ahead. Way ahead, actually, because no animal foods have much fiber. The best foods here are vegetables once again, followed by beans and lentils and some of the more fibrous fruits, like apples and berries. Even some grain foods — like whole-grain breads and pastas — are pretty high in fiber.

Satiety Index

There’s a measurement of satiety called the satiety index, and you want to favor foods with a high satiety index. Anything over 150 is good, and anything over 200 is great. Anything under 100 is terrible.

A related measurement — and one you can find for a much greater variety of foods — is the fullness factor. You can look up the fullness factor of almost any food imaginable in the SELF nutrition database. The fullness factor rates foods on a scale of one to five; anything over three is great, under two should be avoided, and between two and three should be eaten sparingly.

Note that liquid calories are almost uniformly less satiating than solid versions of the same foods — fruit smoothies are less satiating than whole fruit, for example.

Micronutrients, aka Vitamins and Minerals

Unsurprisingly, fruits and vegetables generally have the most vitamins. They don’t all have the same ones though, so you need a variety of them to get all the vitamins your body needs. Most vitamins can be found in other foods — as mentioned, grains have some. Meat has some, and eggs have more, and liver is actually the richest source of vitamin A. But fruits and vegetables are the clear winners here.

The exception is vitamin D — the only good food source for it is fatty fish, but even that doesn’t compare to getting it from the sun. Though, arguably, it’s more of a prohormone than a vitamin.

Mineral sources are a little more diverse, but in general, animal foods tend to have the most of them. Red meat is the best source of iron; milk and sardines are the best sources of calcium. Magnesium is best gotten from leafy greens like spinach, and the best source of chromium is actually brewer’s yeast (followed by beef).

Long story short: fruits, vegetables, and meat. The losers here are grains and other starchy foods, as well as highly processed foods.

Things to Avoid

Processed foods

First, unprocessed foods usually mean more nutrients, as the various ways they are processed can remove many nutrients. White rice doesn’t have the niacin that brown rice has, for example, and white bread doesn’t have the fiber and vitamins that whole wheat bread has.

Second, processed foods sometimes have more toxins. The nitrites in bacon, for instance, raise your risk of colon cancer, albeit not by as much as health alarmists have claimed.

Third, processed foods have a lower thermic effect of food, meaning they effectively have more calories than unprocessed foods. This is because the act of processing them effectively completes part of the digestion process for you — you could sort of think of processed foods as being partially digested already.

Overall, eating more processed foods is associated with higher rates of obesity and death. How do you know how processed a food is? Just ask yourself how much it resembles the food in its natural state. A steak is less processed than a hamburger, an apple is less processed than applesauce, and so on.

Another way of putting this question is: if I picked this plant or killed and dressed this animal myself, would the food I got from that resemble this at all? If the answer is no, the food is highly processed.

Low levels of natural anti-nutrients

One such anti-nutrient is phytic acid. Commonly found in wheat, phytic acid binds to protein and reduces its bioavailability. It also impairs the absorption of minerals like iron and magnesium; as little as 13% of the magnesium in whole-grain bread actually gets absorbed, with the rest being bound by phytic acid. Rice and corn have about one-third of the phytic acid that wheat does.

Refined grains like white rice and white bread have almost no phytic acid or other anti-nutrients — unfortunately, they also have almost no nutrients.

Another antinutrient is lectins, the chemicals which cause beans to make people gassy. They’re found in legumes — beans, lentils and peanuts — and they can damage the lining of the gut.

Even quinoa, that health food so beloved of hippies, has saponins, soap-like molecules that damage the intestines in a similar way to lectins.

Grains like wheat and barley also contain gluten, which people with Crohn’s or celiac disease need to avoid. For the rest of us, though, it’s debatable whether gluten is a problem, or whether the problem is actually FODMAPs.

FODMAPs are a broad class of carbohydrates that most people can’t properly digest. They’re found in a lot of foods, most notably wheat. They’re probably responsible for a huge fraction of all digestive problems, as up to 75% of IBS patients can eliminate their symptoms by going on a low-FODMAP diet.

Lactose is also a FODMAP — about one-third of humans produce enough lactase to digest it well, but the rest should either avoid milk, or only drink it if they supplement lactase to help digest it.

Many fruits and vegetables also have high levels of FODMAPs, including apples, pears, mangos, asparagus, artichokes, onions, celery, and watermelon. It should be noted though that every carbohydrate-containing food has some amount of FODMAPs, and that’s okay — your body can tolerate some of them.

That’s true for all of these anti-nutrients. They need to be minimized, not necessarily avoided altogether. To a certain extent, you can also make up for anti-nutrient consumption by eating more nutrients, too. However, many of these, once absorbed into your body, can also reduce the effectiveness of nutrients that are already in your body.

Many anti-nutrients can also be reduced or neutralized by using traditional preparation methods. Most of the lectins in beans can be removed by washing the beans. The FODMAPs in grains can be transformed into digestible form through methods like souring or sprouting. Sourdough bread and sprouted breads are actually edible even by many people with celiac disease.

Toxins and carcinogens

Preservatives are troubling here — like anti-nutrients, there’s no need to avoid them altogether, but don’t eat a ton of them. Note that salt, while useful as a preservative, is an essential nutrient and not a problem as long as you drink water too, so it doesn’t dehydrate you.

As mentioned earlier, nitrites in heavily processed meats like bacon, baloney, and salami can raise your risk of digestive cancers.

Many fruits and vegetables also contain pesticide residues. Some of these residues sink into the food and don’t wash out, but most lie on the surface of the food and will wash off, so wash your fruits and vegetables before eating them.

Some deep-sea fish have high levels of mercury. The ones with the most mercury are the apex predators — carnivores which eat other carnivores — because they accumulate mercury that gets passed up the food chain. Of the commonly-consumed fish, tuna is the one to watch for here. You can eat tuna, but don’t eat it every day. You can also help your body clear out mercury by consuming selenium — the best source of which is Brazil nuts.

Wheat and soy also have glyphosate and POEA, which may be dangerous.

The biggest offender here, though, is the carcinogens created by overcooking (read: burning) meat. These chemicals are called heterocyclic amines (HCAs) and polycyclic aromatic hydrocarbons (PAHs), and they’re formed when meat is burnt, smoked, cooked until it’s crispy, or cooked over an open flame. So don’t do that.

Unit vs. Continuous Portions

The healthiest foods make it easy to know exactly how much you ate.

Think about chicken nuggets. They’re not the healthiest foods, granted. But if you eat them, it’s easy to count exactly how many nuggets you ate. If you have the package, you can see exactly how many calories that was.

Contrast that to eating chicken pasta. That’s not less healthy per se, but how much pasta did you eat? You can probably only guesstimate, unless you eat a single-serving package, like a Lean Cuisine meal. Even if you weighed the pasta, how would you know how much of that weight was pasta, how much was chicken, and how much was the sauce?

A food has unit portions if it’s divided into clear units, and each unit is more or less identical. In practice, the number of units you eat also needs to be easy to count — meaning it’s less than ten or so. Blueberries are technically units, but if you eat fifty of them, you’re not counting exactly how many you had, and the nutrition information is probably listed in grams rather than the number of blueberries anyway.

This isn’t an excuse to eat shitty packaged food, nor does it mean you need to totally avoid continuously-portioned food. Like any other rule, this is “all other things being equal.” And if you do eat continuously-portioned food, find some way to measure it, whether that’s with a food scale, counting bites, or comparing its size to your hand.

Obviously, this doesn’t matter for foods that are nearly devoid of calories — you don’t need to be careful to avoid overeating Brussels spouts.

So Which Foods Are Healthiest?

Instead, I’ll list the top and bottom three food groups. Here are the three healthiest food groups:

  1. Vegetables — have vitamins, fiber, low calories, very satiating.
  2. Fruits — have vitamins, fiber, slow-digesting sugars, usually pretty satiating.
  3. Seafood, including both fish and shellfish — protein, healthy fats, very satiating, usually few toxins, but be aware of mercury levels.

And here are the three biggest non-obvious losers in this comparison. This is not including full-on junk food like ice cream and French fries, which I assume nobody reading this needs to be told about.

  1. Grains, but most particularly wheat and barley — these have a lot of anti-nutrients, and relatively little protein, vitamins, and minerals. Processed grains also have a low TEF and high caloric density. Remember what I said about traditional preparation methods though; grains become a decent, if not stellar option, when prepared using one of those methods.
  2. Meats that are heavily processed, smoked, or burnt. These have a bunch of toxins, and sometimes also a reduced TEF. The burnt parts of meat, in particular, have been shown to be carcinogenic.
  3. Caloric condiments or additives like mayonnaise, oils, coffee creamer, ranch dressing, honey, BBQ sauce, etc. Some have toxins, but mostly they’re just empty calories with no redeeming nutritional value. Since there’s nothing overtly bad about these, they can be used in moderation if you’re not struggling to lose weight, but they should at least be carefully controlled.

If you want to be super amazingly healthy, incorporate everything discussed in this article into your diet, and do some further research to understand this in greater depth.

But if you want to follow the 80/20 rule — to make a few high-impact changes that will get you like 80% of the way towards a “perfect” diet — just minimize those bottom three foods, along with obvious “junk” food, eat several servings of fruit a day and several servings of vegetables a day, and have seafood 2–4 times a week.

Better Humans

Better Humans is a collection of the world's most…

John Fawkes

Written by

Los Angeles-based personal trainer, online fitness & nutrition coach, and health & fitness writer.

Better Humans

Better Humans is a collection of the world's most trustworthy writing on human potential and self improvement by coaches, academics, and aggressive self-experimenters. Articles are based on deep personal experience, science, and research. No fluff, book reports, or listicles.

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