Baby spinach and lettuce are both naturally fat free and low in calories. You can pile heaping portions of these leafy greens on your plate without feeling guilty. Spinach is delicious steamed or raw and tossed in a cold salad. Lettuce has a higher water content, so you probably don't want to cook it, since it wilts rather quickly. No matter how you enjoy spinach and lettuce, you'll feel better knowing that they are both full of fiber and nutrients.
Baby spinach is a little higher in calories than lettuce. A 4-ounce serving of baby spinach has about 25 calories, while the same amount of lettuce greens has around 15 calories. Even though spinach offers a few more calories, it also has more nutrients, providing slightly higher amounts of fiber, vitamins and minerals.
Vegetables such as baby spinach and lettuce are full of insoluble fiber. This type of fiber makes digestion occur quickly by sweeping out your gut. Insoluble fiber keeps you regular and can help relieve constipation. Women should get somewhere between 21 and 25 grams of fiber daily, while men need 30 to 38 grams, reports MayoClinic.com. You can get about 2.5 grams of fiber from 4 ounces of baby spinach, versus 1.5 grams from the same amount of lettuce.
Baby spinach has nearly three times the calcium content of lettuce. You need calcium to keep your bones and teeth strong. According to the Linus Pauling Institute, a healthy adult should get 1,000 milligrams of calcium daily. Spinach provides approximately 115 milligrams of calcium per 4-ounce serving, versus 40 milligrams from the same amount of lettuce. Although leafy greens add some calcium to your diet, the calcium is not fully absorbed. Oxalic acid in dark green vegetables inhibits some of the calcium absorption. You would need to consume 8 cups of cooked spinach to equal the amount of easy-to-absorb calcium in an 8-ounce glass of milk. Your system does utilize some of the calcium from leafy greens, but you should not rely on them as your primary source of calcium.
Baby spinach also has about three times as much vitamin C as lettuce. Vitamin C is well known for its role in healthy immune function, but it also helps build a skin component called collagen, keeps cells healthy by fighting off free radicals, and helps your body metabolize protein. Each day, women need 75 milligrams of vitamin C, while men require 90 milligrams, the Office of Dietary Supplements reports. You can get more than 30 milligrams of vitamin C from 4 ounces of baby spinach, versus 10 milligrams from the same amount of lettuce.