For optimal health and athletic performance, you need to fill your belly with foods that provide not only calories from macronutrients like protein and carbohydrates, but also adequate amounts of certain must-have micronutrients and vitamins.
Sadly, the so-called "standard American diet" (indeed, it is SAD) is replete with processed foods that don't do a very good job of providing the most important vitamins in optimal amounts. Sure, some vitamins are pumped back into refined foods like white bread, but this is hardly the best way to get what you need. If you buck the trend and focus on consuming nutrient-rich foods, you'll be supplying your body with many of the raw goods it needs to perform at its best.
Part 1 of this six-part nutrient blast focuses on two of the fat-soluble vitamins, A and D, which provide an abundance of health and performance benefits. Not coincidentally, all of these foods also jive with a macro-focused eating approach, so dig in without reservation!
Vitamin A Why you need it, and how much you need
Humans require vitamin A for proper cell growth, which in turn plays a role in forming and maintaining organs such as the heart, skin, and lungs. Vitamin A is also necessary for vision, immune health, and bone health.
There are two main sources of vitamin A: animal sources, which contain preformed vitamin A in the form of retinol, and plant sources, which contain provitamin A carotenoids that the body converts to retinol. The most important carotenoid is beta-carotene which provides the bright orange color in vegetables like carrots and orange bell peppers.
The recommended daily allowance (RDA) for vitamin A is provided as micrograms (mcg) of retinol activity equivalents (RAE) to account for the different bioactivities of preformed vitamin A and vitamin-A precursors. Yeah, its confusing stuff. Just eat a bunch of the foods below and you're good to go. Adult men need 900 micrograms RAE daily, while women should obtain 700 micrograms RAE.
3 ounces = 444% RDA
Perhaps it's time to start serving liver and onions for dinner more often. Since vitamin A is stored in the liver, it should come as no surprise that this organ meat from beef and other animals is a top-notch source. In fact, liver is more concentrated in a variety of nutrients like vitamin B12 and copper than standard cuts of steak. And not to be overlooked are the 21 grams of muscle-sculpting protein in a small 3 oz. serving.
Nobody craves eating liver with a texture akin to shoe leather, so cook it quickly in a smoking hot skillet so that the outside sears while the interior remains tender and still slightly pink. This usually takes about 3 minutes per side. Soaking liver for up to 8 hours in water spiked with salt and lemon juice before cooking can help reduce its notorious strong flavor as well as tenderize the meat.
1 medium potato = 438% RDA
Here's another good reason to be sweet on this tuber. The vitamin A you'll obtain from a sweet potato hails from the plethora of beta-carotene it contains. On top of being a source of vitamin A, beta-carotene acts as an antioxidant in the body which has been linked with a lower risk of developing diabetes.1 Other nutritional perks include ample fiber, vitamin C, vitamin B6, and potassium.
1 cup = 206% RDA
Here's more proof that this hipster green is worthy of its superfood label. Like sweet potato, the vitamin A in kale is mainly in the form of the orange pigment beta-carotene. The high amount of chlorophyll in the leafy green is why it's not orange in color. Other nutritional highlights include plenty of vitamin C and vitamin K.
If you're not a fan of kale's bitter side, a quick steaming or sautéing can mellow its flavor. Also consider stripping the leaves from the stem, which is far more bitter. If that's too much work, buy frozen kale, which is flash-frozen soon after harvest to lock in the beta-carotene and other nutrients.
Of course, the list doesn't end there. Other good sources of vitamin A include pumpkin, carrots, butternut squash, milk, cod liver oil, broccoli leaves, Swiss chard, spinach, goat cheese, turkey and chicken giblets, eel, Bluefin tuna, egg yolk.
Vitamin D Why you need it, and how much you need
To maintain bones of steel, it's essential to get enough vitamin D. This nutrient is necessary for proper calcium absorption, and also impacts the function of compounds called osteoblasts, which are involved in bone formation.
But in recent years, research has shown that vitamin D's role in the body goes well beyond strengthening your skeleton. Adequate vitamin-D status has been linked to everything from improved heart health and brain function to lowered risks of diabetes and obesity.2,3
Many genes in the body are impacted by vitamin D, which is why it has such a varied resumé. Those who like to spend time working up a sweat should take heed of recent data suggesting that vitamin D may help improve athletic performance and muscular strength, reduce inflammation, and even bolster testosterone production.4 This is most pronounced if you're vitamin D-deficient, which well over half of the population is.
Similar to vitamin A, there are 2 forms of vitamin D. Vitamin D derived from sunlight is in the form of vitamin D-3, also known as cholecalciferol. When ultraviolet (UV) rays strike the skin, a molecule in the epidermis—7-dehydrocholesterol—is triggered to initiate vitamin-D synthesis. Vitamin D-3 is also found in animal sources, such as egg yolks and fish.
Vitamin D-2, on the other hand, is derived from mold and yeast. D-2, also known as ergocalciferol, can also be found in plant sources such as mushrooms.
Vitamin D-3 has been shown to be the more potent of the two, and most the likely to exert effects within the body.5 It is also the form used most extensively in clinical trials.
Adults who get minimal sun exposure should aim for at least 600 international units (IU) of vitamin D daily.
1 ounce = 115% RDA
No fish provides more vitamin D than herring; it's one of the best sandwich meats for building muscle, providing plenty of muscle-friendly protein and vitamin B-12 as well.
The availability of fresh herring can be hit or miss, so keep an eye out for pickled or smoked versions, which can instantly up the nutritional ante of your lunch sandwiches.
Canned sockeye salmon
3 ounce = 162% RDA
Here's more proof that the canned-food aisle is somewhere you should spin your wheels. Canned salmon is a convenient way to load up on vitamin D. Other nutritional perks include protein, omega-3 fatty acids, and even calcium if you eat the softened bones. Less expensive canned pink salmon also supplies notable amounts of vitamin D, just not as much as the richer-tasting sockeye. For the sake of the environment, seek out a brand such as Wild Planet that uses only sustainable wild Alaskan salmon.
Other good sources of vitamin D include cod liver oil, sardines, mackerel, fresh sockeye salmon, shrimp, milk, egg yolks, and fortified foods such as yogurt, nondairy milks, orange juice, and cereals.
Very few foods are really packed with vitamin D. Your vitamin-D status is primarily influenced by sun exposure, your location relative to the equator, the amount of time you spend outside, your skin pigmentation, and your use of sunscreen. Have your vitamin-D levels checked by your physician via a simple blood test. If you are deficient, or have suboptimal levels, consult your doctor about supplementing with 2,000-5,000 IU daily of vitamin D-3.
Is there such a thing as too much vitamin A or D?
It's possible to overconsume vitamin A, but you'd have to make a consistent, prolonged effort to do so. Eating copious amounts of liver, guzzling cod liver oil, or overdoing other high-level animal-based sources may lead to hypervitaminosis A (toxic levels of vitamin A). Consuming large amounts of beta-carotene (from orange and yellow fruits and veggies), however, will not make you sick.6
With vitamin D, the ceiling is far higher, and far less clear. Plenty of individuals deficient in vitamin D take upwards of 5,000 IU daily safely, and there's been a lot of clamoring in nutritional circles in recent years to raise the RDA from the current piddling 600-800 IU up to around 4000 IU.
- Sluijs, I., Cadier, E., Beulens, J.W.J., van der A., D.J., Spijkerman, A.M.W. & van der Schouw, Y.T. (2015). Dietary intake of carotenoids and risk of type 2 diabetes. Nutrition, Metabolism and Cardiovascular Diseases, 25(4), 376-381.
- Gonzalez-Molero, I., Rojo-Martinez, G., Morcillo, S., Gutierrez, C., Rubio, E., Perez-Valero, V., Esteva, I., Ruiz de Adana, M.S., Almaraz, M.C., Colomo, N., Olveira, G. & Soriguer, F. (2013). Hypovitaminosis D and incidence of obesity: a prospective study. European Journal of Clinical Nutrition, 67(6), 680-682.
- Munger, K.L., Levin, L.I., Massa, J., Horst, R., Orban, T. & Ascherio, A. (2013). Preclinical serum 25-hydroxyvitamin D levels and risk of type 1 diabetes in a cohort of US military personnel. American Journal of Epidemiology, 177(5), 411-419.
- Dahlquist, D.T., Dieter, B.P. & Koehle, M.S. (2015). Plausible ergogenic effects of vitamin D on athletic performance and recovery. Journal of the International Society of Sports Nutrition, 12(33), 1-12.
- Wolpowitz, D. & Gilchrest, B.A. (2006). The vitamin D questions: how much do you need and how should you get it? Journal of the American Academy of Dermatology, 54(2), 301-317.
- Grune, T., Lietz, G., Palou, A., Ross, A.C., Stahl, W. & Tang, G. (201). Beta-carotene is an important vitamin A source for humans. The Journal of Nutrition, 140(12), 2268-2285.