Most vegetarians consider beans to be a protein food. But most beans are much higher in carbohydrates than protein. Should we think of beans as a protein, a starch, or both?
Vegetarians and vegans lean pretty hard on beans as a source of protein. Even those who sometimes eat meat but also enjoy plant-based meals will often build their meat-free meals around some sort of legume. This is because legumes contain more protein per serving than most other plant foods.
How much protein do beans contain?
But the nutrition profile of legumes is very different from animal protein sources. Eggs, meat, fish, and chicken get anywhere from 50 to 95% of their calories from protein with the rest coming from fat. Legumes, on the other hand, only get about a quarter of their calories from protein. The rest is mostly carbohydrate.
Legumes only get about a quarter of their calories from protein. The rest is mostly carbohydrate.
Soybeans are a bit of an exception—they're higher in both protein and fat and lower in carbohydrate than other legumes.
Peanuts (which are technically legumes) are another exception. They're even higher in fat than soybeans and lower in protein than most beans. Perhaps because of this, peanuts are generally categorized as nuts for the purposes of dietary guidelines, despite their botanical classification.
Can you get enough protein from beans?
Although we often think of beans as being a protein food, the truth is that they provide a lot less protein per serving—and per calorie—than animal proteins.
A 3-ounce serving of cooked chicken breast, for example, provides about 26 grams of protein and about 160 calories The standard serving size for beans is 1/2 cup cooked beans, which provides just 8 grams of protein for around 120 calories.
For every gram of protein in beans, you're also taking in about 3 grams of carbohydrate and a lot more calories.
So, we need to eat a lot more beans to get the same amount of protein as we get from meat. It would take 2 cups of black beans to get the same amount of protein you'd get from 3/4 cup of chicken breast, for example.
But, for every gram of protein in beans, you're also taking in about 3 grams of carbohydrate and a lot more calories.
What about the carbohydrates in beans?
Although beans are relatively high in carbs, these are some of the healthiest types of carbs. The carbohydrate portion of beans is a combination of fiber and starch. But about half the starch in beans is actually what we refer to as resistant starch. That means it resists digestion and absorption in the small intestine and goes on to function much like fiber in the gut.
Perhaps that's why people who eat more beans generally have healthier body weights and lower waist circumference.
The fiber and resistant starch in beans feed the beneficial bacteria in the gut, promote regularity, and help to modulate our blood sugar response to food. They also increase our satiation and satiety after meals, helping us feel full with fewer calories. Perhaps that's why people who eat more beans generally have healthier body weights and lower waist circumference.
Beans also contain phytosterols, plant compounds that are shaped so similarly to cholesterol that they can occupy the cholesterol receptors in our cells. Regular bean consumption is linked with better cholesterol profiles.
How beans fit into your diet
When we build a meal around beans instead of meat, we may need to make some other adjustments to our plates. Because beans contain both protein and starch, it makes sense to reduce other sources of starch to compensate. So, if you're having black-eyed peas instead of blackened catfish for dinner, perhaps you skip the bread or potatoes.
Beans and rice, of course, are a classic combination, in part because of the complementary amino acid profile. But you could have a smaller portion of rice with your beans. Instead of half a cup of beans and a cup of rice, for example, you could switch the proportions. Double up on the beans in order to bump up the protein and reduce the rice to half a cup.
And keep in mind that if you're trying to match the protein content you'd get from meat, you may not have as many calories to spend on other foods due to the extra calories that are riding along with that plant protein.
The downside of beans
Finally, just a word about a somewhat notorious aspect of beans—gas. Beans are particularly rich in fermentable carbohydrates, and while that makes them a feast for our intestinal beasties, it can cause us some digestive discomfort in the form of gas or bloating.
People vary in their sensitivity to the fermentable carbs in beans. Beans are usually avoided in the low FODMAP diet, for example. But those who are not quite as sensitive can often build up their tolerance to these compounds by increasing their bean consumption gradually. Over-the-counter enzyme supplements like Beano or Beanzyme can also be very helpful.