Meat, fish, eggs, and dairy are all good sources of protein. Different foods contain different mixes of other energy-producing nutrients, though.
Protein: Non-Animal Based
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If your diet doesn't include a lot of meat or other animal products, you may need to increase your intake of plant-based proteins in order to avoid fatigue.
Fruits
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Fruit can be an excellent source of vitamins and minerals, including those that help your body produce energy. Fresh, whole fruit is best, since it can lose vital nutrients as it gets older or as it's dried.
Vegetables
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Vegetables contain multiple energy-producing nutrients, and some will even give you a little bit of protein (although not nearly as much as sources like meat, eggs, dairy, nuts, and beans).
Grains
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Grains are a source of carbohydrates for quick energy as well as some nutrients for sustained energy
Milk Substitutes
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Popular substitutes for milk contain some energy-producing nutrients, either naturally or through fortification.
A Note on Caffeine
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Caffeine gives you quick energy, but it's a stimulant, which means it speeds up your body's processes rather than nourishing your cells. It's not an inherently bad thing—in fact, coffee and tea both have some health benefits.