What Exactly Makes a Food Healthy?

Probably literally a million lists of healthy foods have been written, but I don’t know if I’ve ever seen anyone take a step back and explain exactly what qualifies a food as “healthy.”  So I decided to do that.

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- Lower is Better

This assumes that, like most people, you’re either trying to lose weight, or concerned about preventing fat gain, or at the very least you’re more likely to overeat than undereat.  If any of those are the case, foods with lower caloric density are healthier. 

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

Looking at a couple of 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 mixed nuts have 180 calories per 28 gram serving, or 6.43 calories per gram.  So the meat is a clear winner here. 

The least calorically 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.   

Low caloric density- along with a high satiety index, discussed later- is particularly important for snack foods.  Ideally you wouldn’t snack between meals at all, but if you do, the snacks need to be low-calorie.

Protein Content- Higher is Healthier

High protein is better than low protein, for a few reasons.  First, protein has the highest thermic effect of food.  Second, it fuels muscle protein synthesis- so more of those calories will go to building lean tissue, rather than fat.  And third, foods higher in protein are more satiating.

Not all proteins are created equal.  Animal proteins are superior to plant proteins across the board, for a couple 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 sources are lean meats and fish, followed by fatty meats, fish and eggs, followed by meat substitutes like tofu or tempeh, then high-protein vegetable foods like beans, lentils, and almonds.

Dietary Fiber- More is Better

Dietary fiber is really important, and you should be getting a lot of it- like 30-50 grams a day.  Like protein, it contributes to satiety.  It also provides two other key benefits, depending on which kind of fiber we’re talking about.

Soluble fiber gets absorbed into the bloodstream and clears plaque out of your arteries.  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 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.


Most people have heard that unprocessed foods are superior to processed foods, but don’t know why.  So here’s why.

First, unprocessed foods usually more more nutrients, as the various ways they’re 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. 

Satiety Index- High Is (Usually) Better

Going off of all those previous items, the best foods will make you more full and keep you full longer.  They’ll be more satiating- on a per-calorie, per-gram, and per-cubic centimeter basis. 

There’s a measurement of satiety called the satiety index- 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.  It’s rated one through 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

Healthy foods have the most micronutrients- a term that collectively encompasses vitamins, minerals, and any other kind of nutrient that’s measured in micrograms or milligrams rather than grams. 

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 though- 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 it arguably is 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 though, 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. 

Low Levels of Natural Anti-Nutrients

Some foods contain anti-nutrients which damage your gut and impair absorption of other nutrients.  Unsurprisingly, they also cause digestive issues like IBS, gas, diarrhea and constipation. 

One such anti-nutrient is phytic acid.  Commonly found in wheat, phytic acid binds to protein and reduces its bioavailability.  It also impairs absorbtion 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. 

And then there are FODMAPs, 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. 

Lack of Artificial Toxins and Carcinogens

Some foods have artificial toxins, either from various types of processing or cooking. 

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 its crispy, or cooked over an open flame.  So don’t do that. 

Unit vs Continuous Portions

Unlike everything else on this list, this one has nothing to do with the nutritional content of food.  Instead, it’s a practical consideration that’s widely discussed in the research but rarely mentioned in popular media.

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 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 like 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 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?

Since your body needs a tremendous variety of nutrients, it would be pointless to give you a list of like five or ten specific foods here.  Hopefully you understand by now why “superfoods” are bullshit, but some foods are clearly healthier than others.

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 losers in this comparison.  Not including full-on junk food, which I assume nobody needs to be told about. 

  1. Grains, but most particularly wheat- has a lot of anti-nutrients, relatively few nutrients.  Processed grains also have a low TEF.  Remember what I said about traditional preparation methods though.
  2. Meats that are heavily processed, smoked, or burnt- has a bunch of toxins, sometimes also a reduced TEF. 
  3. Caloric condiments or additives like mayonnaise, coffee creamer, ranch dressing, honey, BBQ sauce, etc.  – Some have toxins, but mostly they’re just empty calories with no redeeming nutritional value. 

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, eat several servings of fruit and as many vegetables as humanly possible, and have seafood 3+ times a week.