On Nutrition

I’m willing to bet you already know that eating more fiber is good for heart health. But do you know why? While the answer is somewhat complicated, the solution is not.

First, let’s deal with a little terminology, because if your brain gets too bogged down in parsing the differences between dietary fiber, soluble fiber, insoluble fiber and fermentable fiber, it’s easy to give up and forget about upping your fiber intake at all.

Soluble fiber disperses in water (or digestive juices), and includes fiber from pulses (beans and lentils), barley, oats, some fruits and vegetables and psyllium. Insoluble fiber comes from whole grains, especially the bran, and vegetables. However, the terms soluble and insoluble have somewhat fallen out of favor, because there are other qualities that matter more, such as whether soluble fiber forms a viscous gel, or if the fiber is fermentable.

That said, the main thing to focus on is getting more dietary fiber — the overarching term for naturally occurring fiber in whole plant foods such as pulses, fruits, vegetables, whole grains, nuts and seeds. A good proportion of that fiber will also be fermentable, which means friendly bacteria in our large intestine (colon) digest it for us, producing many byproducts of that offer us health benefits.

So, how much fiber are we talking about?

The recommended intakes for dietary fiber in the Dietary Guidelines for Americans were set with heart health in mind, said Joanne Slavin, Ph.D., a registered dietitian and a nutrition professor at the University of Minnesota who has done significant research in the areas of dietary fiber and health.

Speaking at the recent annual meeting of the Academy of Nutrition and Dietetics, Slavin said results from large, prospective cohort studies — which enroll participants to collect information about how they eat, and monitor their health for years to look for connections — demonstrate that getting 14 grams of dietary fiber per 1,000 calories significantly reduced the risk of developing cardiovascular disease. For a 2,000-calorie diet, that would be 28 grams of fiber.

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If you’ve long wondered why standard recommendations are that women need at least 25 grams of fiber per day but men need at least 38 grams, it’s based on the assumption that the average woman is eating 1,800 calories per day, while the average man is eating 2,500 calories per day. Unfortunately, 90% of Americans only get 15 grams daily, on average.

Is it bad to get more fiber than that? No. Slavin said there’s no upper limit for dietary fiber intake, and research on vegetarians consuming up to 80 grams per day has found no issues. Resistant starch — literally starch that resists digestion, such as the starch found in pulses, oats and cooked and cooled rice, pasta and potatoes — is similarly well tolerated. Not as well tolerated are fructo-oligosaccharides, a type of fermentable fiber found in garlic, onions, leeks, blue agave, asparagus, chicory root and bananas. In excess, fructo-oligosaccharides can cause diarrhea, and some people with irritable bowel syndrome (IBS) find they can’t tolerate it at all.

How does fiber help the heart?

Eating more dietary fiber is associated with lower risk of heart disease, heart attack and stroke (aka cardiovascular disease). Since the fiber in our food doesn’t have a direct line to the heart, what’s the connection?

  • Fiber is a marker of a healthy diet, Slavin said. In other words, if your diet includes a lot of dietary fiber, it’s because you’re eating a lot of plant foods, which also contain vitamins, minerals, antioxidants and phytochemicals, many of which may prevent or reduce chronic inflammation, another contributor to cardiovascular disease. Fiber also helps you feel pleasantly full after a meal, which can help prevent eating more calories than your body needs.
  • Viscous soluble fiber from oat bran, rolled oats, whole wheat flour, whole grain barley, barley bran and psyllium can directly lower cholesterol levels.
  • Fermentable fiber provides the raw materials for compounds that have benefits for cardiovascular health.

A (healthy) gut punch to the heart

Everything we eat, if it’s not absorbed, is either fermented by microbes in the large intestine (our gut microbiota) or excreted. “Anything that gets down into the large intestine can be acted upon,” Slavin said, adding that there can be negatives or positives to that based on what types of byproducts are produced. For example, when we eat plant foods, the microbiota use fermentable carbohydrates and fiber to make short-chain fatty acids, which can have a number of health benefits, including helping lower cholesterol, as well as vitamin K and biotin. On the other hand, certain microbes can also digest protein and fat, and the resulting byproducts have been implicated in cardiovascular disease.

3 ways to boost your fiber intake

  • Swap some animal protein for plant protein. Beans, lentils, soy foods, nuts and seeds all contain fiber along with protein and heart-healthy fats.
  • Include a vegetable or fruit (or both) in every meal or snack. Yes, this sounds simple, but are you doing it? Keep in mind that an apple or some carrot sticks don’t make a sufficient snack — pair them with some plant protein for staying power, such as nuts with that apple and hummus with your carrot sticks.
  • Make at least half your grains whole — oats, brown rice, farro and wheat berries are a few examples. This is not new advice, but, again, are you following it?

Keep in mind that increasing your fiber intake too much too soon can feel uncomfortable, so go slow to keep excess gas and bloating to a minimum. It’s also a good idea to drink more water as you start eating more fiber, especially if you tend to get constipated.