The increasing popularity of low-carb and ketogenic diets has some nutrition professionals concerned that people may not be consuming enough vegetables, especially the all-important greens. Ketogenic diets have plenty of room for fiber, but some people may choose to get that fiber in the form of cauliflower substitutes for rice and mashed potatoes, or muffins and biscuits made from almond and coconut flour. Whether they’re on a reduced-carb diet or not, are people missing out on something if they skimp on greens?
Green vegetables, be they leafy greens like spinach, collards and lettuce, or other green veggies like broccoli, asparagus, celery and brussels sprouts, are one of the only food categories the various warring nutritional factions seem to agree on. Whether someone prefers a Paleo diet, keto, vegetarian, vegan, or low fat, these foods can safely be on the menu. On their own, they’re obviously low in both fat and carbs. For those on higher fat diets, they make excellent vehicles for melted cheese or a generous pat of butter. For those who prefer low fat, consuming a larger quantity of these vegetables is a good way to feel full on fewer calories and virtually zero fat.
Green vegetables, the dark leafy ones in particular, are high in folate, magnesium, potassium, calcium and vitamin K1. (Good news, by the way: a study from June of this year showed that patients taking warfarin need not drastically reduce their intake of leafy greens that may interfere with the blood thinning effects of this drug. In fact, in this 24-week randomized controlled trial, patients who were instructed to increase vitamin K intake by at least 150 mcg/day showed improved anticoagulation stability compared to patients given general dietary information without emphasis on vitamin K. A larger proportion of patients who received counseling specifically about increasing vitamin K intake spent significantly more time in the therapeutic range for anticoagulant therapy.)
Including greens in the diet goes beyond the benefits of the greens, themselves. Interactions or synergies between them and other dietary factors might elevate the effects of these other factors. This was shown in a study of African Americans, among whom higher intake of dark green vegetables was shown to enhance the effects of omega-3 supplementation. In subjects taking 3 grams of n-3 per day for six weeks (2g EPA and 1g DHA), those who reported consuming more dark green vegetables (via food frequency questionnaire) had a better response to n-3 supplementation, evidenced by an increase in red blood cell EPA concentration, decrease in triglycerides, and decrease in monocyte concentration of leukotriene B4, an inflammatory metabolite of arachidonic acid.
It’s often argued that the non-heme iron found in plant foods is not as bioavailable or as effective for supporting body iron stores as the heme iron found in animal foods, and that many people do not covert the vitamin A precursors in plant foods to true retinol/retinal effectively. While this may be true, it doesn’t mean plant foods have no effect whatsoever on body nutritional status. A study on women in Tanzania showed that higher intake of dark green leafy vegetables correlated with higher hemoglobin, iron status and serum retinol. It may be that in places where animal foods are less abundant, greater intake of certain nutrient-rich vegetables can make up at least in part for this shortfall, especially compared to diets higher in cereal grains, in which a greater presence of antinutrients (such as phytic acid) may reduce the bioavailability of critical minerals.
Another point working in greens’ favor is that they’re very affordable. While grass-fed meats, organic coconut butter, eggs from pasture-raised hens and other high-quality foods may be beyond the financial reach of some patients, greens are budget-friendly for just about everyone. Cabbage often goes on sale for less than fifty cents a pound; broccoli crowns can be regularly found for about a dollar fifty a pound and frozen greens may be an even more affordable choice, often going on sale for as little ninety-nine cents a package.
Of course, nutrient content and affordability are no guarantee that people will choose to consume these foods. Some people simply don’t like the taste, particularly those who are “supertasters” and have extraordinary sensitivity to the bitter flavors in things like kale and chard. For the most part, modern food processing has taken a dark turn toward ever-increasing amounts of refined sugar and industrial seed oils, but this doesn’t mean “processing” is automatically bad. After all, depending on how you define the word, nutritious foods that have been consumed for hundreds if not thousands of years—like yogurt or sauerkraut—are “processed.” In fact, cooking can be considered a form of processing, so anything not eaten raw can be said to be “processed.” Semantics aside, dehydrating/drying and pulverizing green vegetables into powders is a way to get adults and kids alike to eat more of them, especially if the powder is a touch sweet, either from being combined with powdered fruits, or sweetened with stevia or erythritol. It might be better to eat things in whole food form, but for those who turn their noses up at that, adding powdered greens to water or some other beverage is a good way to get some of the nutrients they might otherwise miss out on.
All this being said, we would be remiss if we didn’t acknowledge that there are, in fact, people who may not fare quite so well with increased greens intake—or increased intake of fibrous vegetables of any kind. In what at first may seem paradoxical, increased fiber can worsen constipation in some individuals. Getting more fiber is a common recommendation for individuals with constipation—to “get things moving,” so to speak. But if lack of fiber isn’t the cause of the constipation, adding more fiber may not help and instead could actually make things worse. (When there’s already a traffic jam, the last thing you’d want is to add more cars!) A fascinating study from a few years back showed that in adults with idiopathic constipation, reducing or even altogether eliminating dietary fiber improved symptoms, including increasing bowel movement frequency.
So, as in seemingly everything in functional medicine and nutrition, there are no blanket recommendations that apply to everyone under all circumstances. The art of these professions lies in tailoring individualized approaches to help each patient move toward optimal health.