Newsworthy diet trends have a tendency to take “conventional” diet advice and turn it on its head for effect. Fat free? Now go high-fat, low-carb. Monitor saturated fat? Now add coconut oil to everything. The latest food group to get this flip-flop treatment is whole grains. Though the Dietary Guidelines for Americans—created for the USDA by a panel of experts based on the body of nutrition evidence—have long recommended increasing whole grain intake as part of a healthy diet, many blogs and diet books are eschewing that advice, denouncing whole grains as a source of "antinutrients." Do they have a point? An examination of the evidence will separate the wheat from the chaff.
For low-carbohydrate diet enthusiasts, carbs are the problem with grains (see more on that here). However, some diet authors and bloggers denounce whole grains as a source of “antinutrients” that supposedly promote inflammation and prevent effective digestion. For these advocates, whole grains are not a poor choice because of their energy or carbohydrate density, but because of certain molecules, known as lectins and phytates, present in grains.
So are lectins and phytates antinutrients? Is everything we thought we knew about nutrition wrong once again? The answers are: Errrr, sort of? And no.
Lectins are the name given to a variety of plant proteins that have a similar function: they can bind to specific carbohydrates. These lectins can be used by plants in multiple ways, including playing a role in a plant’s defense system against predators. When used as part of the defense system, lectins can bind to molecules present in the cell walls of attacking bacteria or fungi and destroy them. Lectins are found in numerous plant foods, including grains, legumes, fruits, and vegetables.
Phytates are phosphorus-containing acids (phytic acid) bound to minerals. They are also found in plants, including (surprise!) whole grains, where they play a role in germination.
Proponents of grain-free diets, such as the paleo diet, Whole30, “Wheat Belly,” low-carb diets, and most recently, lectin-free diets, believe that whole grains are inflammatory. They state that the lectins and phytates in foods lead to conditions like “leaky gut” and chronic inflammation, which in turn, they claim, lead to chronic disease. In fact, some folks take this argument so far as to recommend refined grain products (like white bread and white rice) over their whole grain counterparts. This flies in the face of US dietary guidelines, which recommend increasing whole grain consumption and making at least half of your grain consumption from fiber-filled whole grains. Why do they make these claims? Is there any truth to it?
Yes, there is truth to the idea that lectins and phytates can have adverse effects, but there are some major caveats. “While most [lectins] are safe to eat,” says Anastasia Bodnar, plant geneticist and Policy Director of Biology Fortified, Inc., “some plant lectins are toxic due to their ability to bind certain carbohydrates in our bodies. For example, ricin from castor beans is a lectin.” Some lectins in high concentrations in edible foods (especially in undercooked legumes like kidney beans) can cause severe stomach pain and vomiting. However, if you properly cook these foods, you’ll avoid these uncomfortable outcomes.
Further, the low concentrations of lectins in edible grains and grain-based foods are not associated with negative health effects. A 2014 research review in the journal Cereal Science concluded that the current data on lectins does not support negative health effects as people consume them normally in foods. “The current scientific evidence is strong and consistent to suggest that whole grains have beneficial effects in individuals with no genetic predisposition for celiac disease, despite the dietary lectin content,” the review authors write. “Despite numerous speculative assumptions that wheat germ lectins cause intestinal damage and disease, there is at present neither evidence that this is the case nor reason to recommend the healthy population to abstain from whole grain food products.”
In fact, numerous studies show whole grain intake is associated with health benefits, including a significantly lower risk for cardiovascular disease and type 2 diabetes (more on that later).
The major cited downside to phytates is micronutrient malabsorption. During digestion, phytic acid can bind to micronutrients such as zinc, magnesium, and iron and cause reduced absorption. This phytate concentration truly can be a problem, but primarily in developing nations with high food insecurity where the vast majority of food calories comes from grains, and mineral deficiencies are a common result of the lack of diversity in overall diets. For example, research shows that, in certain developing countries, existing zinc deficiencies may be exacerbated by high phytate intake.
However, in industrialized nations, with a plentiful and diverse food supply, as well as food fortification, mineral malabsorption from phytates is much less of a problem. Sometimes when diet bloggers and authors talk about the dangers of phytates, they talk about the molecular mechanisms and look at studies that show mineral deficiencies seen in developing nations with diets very high in grains and very low in animal products, which aren’t reflective of modern western diets. All in all, phytates aren’t a good reason for giving up whole grains.
There are some illnesses—like celiac disease—that call for the elimination of specific foods. But these issues don’t affect the majority of folks, and diets that require eliminating food groups should be done with the help of a health professional, such as your physician or a registered dietitian.
In a 2016 meta analysis in the British Medical Journal combining results from 45 prospective studies (these are observational studies that collect data about participants’ food intake and then track their health outcomes over time), researchers found that there was a dose-dependent relationship between whole grain intake and cardiovascular disease; that means greater intakes were associated with greater reductions in risk. Similarly, a 2013 meta analysis in the European Journal of Epidemiology combining results from 16 observational studies found an inverse relationship between whole grain intake and risk of diabetes—increased whole grain intake correlated to decreased risk of diabetes.
But what exactly is it about whole grains that helps prevent chronic diseases like cardiovascular disease and diabetes? That’s a hard question for researchers to answer, and here’s why: The strongest evidence for health benefits of whole grains comes from observational studies, which follow the diet habits and long-term health outcomes of participants, but can’t necessarily determine whether the whole grains actually cause better health outcomes.
That said, there’s evidence to support numerous mechanisms of whole grain consumption as being good for your health. Research suggests that the increased soluble fiber content of whole grains may help lower blood lipids by preventing cholesterol reabsorption in the gut, and may promote good gut health by providing prebiotics, a type of fiber that feeds healthy gut bacteria. And, in some studies, participants on diets rich in whole grains have shown better results in insulin sensitivity, blood pressure, and blood cholesterol compared with those who ate diets higher in refined grains. Whole grains also naturally contain several B vitamins and minerals, which are removed in refined carbohydrates (although in most refined flour products in the U.S. and Canada, vitamins and iron are added back via enrichment).
Overall, the presence of lectins and phytates in whole grains are not a problem in a balanced diet (one with sufficient calories and micronutrients) when foods are properly prepared.
Katherine Pett is a registered dietitian with a master’s degree in nutrition biochemistry and epidemiology. She writes about nutrition at thenutritionwonk.com. She currently an employee of Conagra Brands, maker of consumer food products including several whole grain foods.
