Sluggish and Low on Energy? You Might Be Missing One of These Key Nutrients

Nutrient deficiencies are more common than you think: Even when you’re eating a healthy diet, you can unknowingly miss out on crucial vitamins and minerals. And over time, these nutritional shortages can dampen your vigor and leave you feeling foggy, lethargic, and in need of a nap. Failing to get certain nutrients from food can completely zap your energy levels.

If you’ve been feeling fatigued lately, check in on your diet and see if you’re getting all of the energy-fueling nutrients you need day in and day out. Here are six must-have vitamins and minerals, plus tips on how to boost your intake when you’re coming up short.

1. Magnesium

This mineral goes way beyond building strong bones. Magnesium plays a central, though often unrecognized, role in whole-body vitality. It’s essential for producing adenosine triphosphate (ATP), a molecule that carries energy within cells, and it impacts your stamina at a cellular level. Magnesium is also involved in muscle contraction and relaxation, protein synthesis, hormone secretion, electrolyte balance and hundreds of other physiological processes that ultimately influence vigor and verve. 

Plus, magnesium eases stress, anxiety, and depression, which are all linked with higher rates of fatigue and lethargy. And by interacting with neurotransmitters that soothe and calm the nervous system, it promotes sounder slumber, meaning you sleep better and wake up peppy and ready to go when you’re getting plenty of magnesium. 

Deficiencies are common, however. Antibiotics, pain killers, birth control pills, too much sugar or caffeine, and ongoing physical or mental stress are all factors that can deplete magnesium, and studies link low levels with diminished stamina and faster fatigue.

Foods rich in magnesium include: Spinach, kale, collards, avocados, pumpkin seeds, almonds, cashews, beans, lentils, tofu, and dark chocolate. 

RELATED: New Study: Marathon Performance Linked to Fats, Potassium, Magnesium in Diet

2. Complex carbs

Carbohydrates are the body’s primary source of stamina-sustaining fuel. The carbs you eat are turned into glucose, a simple sugar that’s used by cells to power their operations. Any glucose that’s not used for energy is converted to glycogen, a network of connected glucose molecules that’s warehoused in the liver and muscles. In the absence of adequate dietary glucose, the body breaks down glycogen for fast fuel. 

Simple carbohydrates (bread, rice, pasta) are hastily digested and rushed into the bloodstream. Complex, fiber-rich carbs are broken down at a slower pace, for balanced, all-day energy to enhance endurance and stamina—especially during activities like sprinting, strength training, and HIIT routines that require short bursts of intense movement. 

And because glucose is the brain’s preferred fuel, carbs promote mental clarity. When glucose levels dip, focus and concentration decline. Some research suggests ultra-low-carb diets impair cognition, learning and memory, though other studies show low-carb regimens improve attention and the ability to stay on task. 

Foods rich in complex carbs include: Beans, peas, lentils, oatmeal, butternut squash, acorn squash, sweet potatoes, barley, and quinoa.

RELATED: Your Complete Runner’s Guide to Carbohydrates

3. Protein

Carbs are the body’s go-to fuel, but you need plenty of protein to build and repair muscles and power through your day. Protein is broken down slower than carbohydrates, providing balanced and sustained stamina. Plus, research links high-protein meals with significant increases in endurance and energy. 

Protein-rich foods that contain healthy fats and complex carbs (like almond butter, hummus, and eggs) also stabilize blood sugar and fight fatigue. Additionally, certain amino acids are directly involved in cellular energy production. Besides physical get-up-and-go, protein also supports the synthesis of norepinephrine and dopamine, neurotransmitters associated with alertness, drive, and motivation. Studies show high-protein meals enhance vigilance and focus and improve reaction time. 

Protein deficiencies are uncommon, but vegans, uber-athletes, or people with digestive disorders may require more. If you’re on a meat-free diet, you can supplement with concentrated sources; think plant-based protein powder combos (like rice and pea) that cover all your amino acids to form a complete protein. 

Foods rich in top-tier protein include: Grass-fed beef, chicken, seafood, nuts, yogurt, tofu, beans, peas, lentils, cottage cheese, and protein powder.

RELATED: This High-Protein Baked Oatmeal is Your New Go-To Breakfast

4. Potassium

Your weak, foggy, unfocused self might be in need of more potassium. This essential mineral acts as an electrolyte, carrying a tiny electrical charge that triggers nerve and cellular functions throughout the body. Potassium plays a key part in regulating heart rhythm, fluid balance, blood pressure, and muscle contractions, and it’s required for converting blood sugar into glycogen. Low levels provoke crampy, weak muscles and hasten fatigue. And when potassium drops below a certain point, electrical signals in the brain are disrupted, manifesting in sluggish thinking, confusion, and all-around brain fog. 

Because potassium balance is tightly controlled by the body, life-threatening deficiencies are rare. But even relatively small shifts in potassium concentrations can sap strength, stamina, and mental clarity. Prolonged exercise, intense heat, and excessive sweating significantly deplete potassium, as do diuretics and other medications. And on-the-go eating habits mean many of us are lacking. When sodium levels increase, potassium declines—so salty, processed, and fast foods encourage deficiencies.

Foods rich in potassium include: Potatoes, sweet potatoes, beet greens, chard, spinach, mushrooms, pinto beans, lima beans, watermelon, tomato paste, and coconut water.

RELATED: How to Fuel Long Runs with Real Food

5. Iron

Run-down and weary all the time? You may need more iron. This important mineral is involved in numerous physiological functions linked with stamina, focus, and vitality. Cells require iron to make ATP and hemoglobin, necessary for transporting oxygen in the blood. Low levels disrupt hemoglobin production, impacting blood’s ability to ferry oxygen and nutrients to hungry cells, sapping strength. Iron also influences the synthesis and signaling of neurotransmitters linked with attention, drive and motivation; insufficient stores provoke weakness, fatigue and lethargy. 

Iron deficiencies are common, especially in women, vegetarians, and vegans. Stress, poor diet, and heavy drinking are all factors that can deplete iron, and some foods  (like coffee, tea, and milk; tannins in wine and apples; oxalates in chocolate and leafy greens) hamper its absorption. And if you’re on a meat-free diet, non-heme iron in plants is less available than heme forms found in animal products. Plus, phytic acid in legumes, grains, and nuts impairs your ability to absorb iron, as well as zinc, calcium, and other minerals. 

To maximize the iron in foods you’re eating, soak legumes and grains before cooking to reduce phytic acid and combine non-heme iron with foods high in vitamin C; it’s shown to boost iron absorption. 

Foods rich in iron include: Grass-fed beef, organ meats, seafood, shellfish, white beans, blackstrap molasses, spinach, beet greens, lentils, and soybeans. 

RELATED: The Female Runner’s Complete Guide to Iron

6. B vitamins

If you’re tired, moody, and mentally muddled, it could be a sign of B vitamin deficiency. As a group, the eight primary B vitamins regulate a range of physiological functions, acting as coenzymes in cellular energy metabolism and influencing ATP synthesis and red blood cell formation. They’re essential for nervous system function, neurotransmitter production, and cognitive performance, and research shows subpar levels accelerate fatigue, impair concentration and alertness. 

Though B vitamins are abundant in food, deficiencies are more common than you might expect. They’re not stored in the body, and low levels are linked with lethargy, fuzzy focus, and diminished physical and mental stamina. Stress, sleepless nights, medications (like birth control pills), heavy drinking, and a not-so-healthy diet can deplete your supply. And since vitamin B12 occurs only in animal products, vegans are likely to be lacking. If you follow a strictly plant-based diet, take a B12 supplement; sublingual methylcobalamin forms are better absorbed and utilized.

Foods rich in B vitamins include: Spinach, collards, turnips, lentils, beans, shellfish, sunflower seeds, eggs, turkey, and nutritional yeast.

RELATED: Are You Actually Absorbing the Nutrients from the Foods You’re Eating?