It’s important to get your greens in, but keeping a healthy diet doesn’t always mean you’re getting all of the nutrients you need. Some nutrients actually maximize or interfere with one another’s function within your body—so depending on what you eat and when, you may be boosting or missing out on the benefits of those healthy foods (and supplements!).
To get the full nutrient bang for your buck and prevent wasting any of the good stuff, you’ll want to pair some nutrients together and avoid eating others together.
1. Vitamin D + Calcium
Here’s what’s going on: “The majority of the calcium in our body is stored in our bones, and vitamin D helps absorb, carry, and deposit that calcium into our bones,” she says. So if you’re short on vitamin D, your body won’t be able to carry the calcium into the bones to be absorbed and stored, she adds.
Vitamin D can be found in animal-based foods like eggs, fatty fish, dairy, and fish oils, while calcium can be found in dairy, beans, and kale, she says. You can knock out both of these nutrients at once by eating dairy—but otherwise try to pair calcium-rich foods with vitamin D-rich foods. (Good to know: A lot of foods, like milks and cereals, are fortified with vitamin D.)
Another way to better absorb calcium: Pair it with inulin-type fructans (a type of nondigestible carb), suggests research published in The Journal of Nutrition. You can find insulin-type fructans in wheat germ, bananas, garlic, onions, and leeks. So consider adding some wheat germ or banana slices to your morning yogurt.
2. Vitamin D + Healthy Fats
In addition to pairing vitamin D with calcium, one of the best ways to increase your absorption is to ensure you are getting enough dietary fat, says Andrea Conner, M.P.H., R.D.N., C.D.E.
“Vitamin D is fat-soluble, meaning it needs fat to be absorbed,” says Conner. For that reason, she always recommends pairing vitamin D-rich foods with a high-quality fat, like olive oil, flax seeds, avocado, fish, chia seeds, or nuts. Just a couple teaspoons of oil or a handful of nuts will do the trick, she says.
Those healthy fats will also help you get the most benefit from carotenoid-packed foods (think yellow, orange, and red produce, like peppers, carrots, and tomatoes), according to research out of Ohio State University. The fats make plant compounds like beta-carotene (which we convert into vitamin A) and lycopene more available to our body.
3. Iron + Vitamin C
Iron can both enhance and mess with the absorption of other nutrients, says Kelly R. Jones, M.S., R.D.N., C.S.S.D., L.D.N. So, while the mineral is a pretty important staple in our diet, what you eat iron with is especially important.
The biggest concern about iron absorption is whether you’re getting it from plant or animal sources. “Iron from animal foods, like beef, is much more absorbable than iron from plant foods, like spinach, beans, and whole grains,” says Jones. That’s because other factors in plant-based sources can inhibit your uptake of iron—like oxalic acid in spinach, she says. So vegetarians and vegans who get their iron from plant-based sources should be extra vigilant about what they eat it with.
This is where vitamin C comes in handy, Jones says. (You’ll find vitamin C in all sorts of citrus fruits, red peppers, kale, and broccoli.) The vitamin enhances your absorption of iron, so Jones recommends that vegetarians pair the two together whenever possible. “It can be as simple as adding lemon juice to their water while eating a plant-based meal,” Jones suggests. Or just make sure vitamin C-containing veggies make it onto your plate along with those beans or whole grains.
4. Vitamin B12 + Acid
As with iron, any acidic food can also help increase your absorption of vitamin B12, says Jones.
“We all produce stomach fluid in response to hunger and smelling and eating food, and part of that stomach juice is hydrogen chloride, which helps us break down protein and absorb B12,” explains Jones. Adding acidic foods, like vitamin C-containing citrus fruits, can help boost the acid in your stomach needed to absorb that B12, which is found in organ meats, fish, eggs, and feta cheese. Jones likes to spritz lemon on fish or add it to salad dressings to help that B12 get to where it needs to go. You can also sip on some apple cider vinegar and water to boost that acid, she suggests.
1. Iron + Copper + Zinc
All three of these nutrients are essential for a healthy diet, but they can interfere with one another’s absorption if consumed together in high amounts, says Jones.
“Because the same receptors in the digestive tract absorb zinc, iron, and copper, if there is an excess of one nutrient, it crowds out the others from making it through the intestinal wall,” she explains.
You know you’ll find iron in meats, spinach, beans, and whole grains. But what about copper and zinc? Copper is found in shellfish, organ meats, whole grains, beans, and nuts, while zinc is found in oysters, red meat, and poultry. You’ll want to avoid eating too much of these foods at one time, but the real concern here is with iron supplements. If you take an iron supplement, leave a few hours between popping your pill and eating a meal that includes zinc or copper-containing foods, says Jones. She recommends taking your supplement with a piece of fruit, crackers and hummus, or avocado toast, which are all low in zinc and copper.
2. Calcium + Iron
Like with copper and zinc, iron competes with calcium to be absorbed in your intestines, so these two minerals reduce each other’s uptake in your body. (And this impairment can occur in either supplement or food form, according to research published in the International Journal for Vitamin and Nutrition Research.)
The competition between these two nutrients is particularly serious for people with certain health conditions. Many people with anemia are told to avoid taking their iron supplements for up to four hours after eating something high in calcium (like a bowl of yogurt or cottage cheese), says Jones. Similarly, women with osteoporosis should avoid taking calcium supplements within a few hours of eating foods high in iron (like beef, spinach, or beans.)
So, you might want to consider avoiding combos that go heavy on meat and cheese, especially if you’re suffering from one of these health conditions.
3. Vitamin E + Vitamin K
Sadly, there are a couple circumstances in which you should turn down avocado toast: If you’ve just taken a vitamin K supplement or noshed on a bunch of cruciferous veggies. Why? Vitamin E (which is found in avocado) can mess with vitamin K (which is found in cruciferous veggies and many supplements).
“Excess amounts of vitamin E can actually reduce the absorption of vitamin K, which is important for blood clotting, calcium metabolism, and bone mineralization,” says Elizabeth Ann Shaw, M.S., R.D.N., C.L.T. While moderate amounts in combination—like spinach (vitamin K) and oil-based salad dressing (vitamin E)— shouldn’t do much harm, higher doses can be problematic, she says. Just be sure to stick to a tablespoon of oil in your salad dressing, she adds.
Foods rich in vitamin E include wheat germ oil, grains, nuts, seeds, green leafy vegetables, avocado, and dried prunes, while veggies, like broccoli, kale, spinach, cauliflower, cabbage, and Brussels sprouts are high in vitamin K.