Red leaf lettuce naturally qualifies as a calorie-free food, according to U.S. Food and Drug Administration regulations. It's also fat-free and consists primarily of water. These nutritional qualities create low-energy density, which makes red leaf lettuce valuable for weight management. You can eat a reasonable portion and feel full, while getting a boost of vitamins A and K.
Macronutrients in Red Leaf Lettuce
Red leaf lettuce is easily recognized by its loose clump of leaves tinged with shades of red to dark reddish-purple. It has about the same nutritional profile as green leaf lettuce and romaine, but romaine has double the vitamin A. Red leaf lettuce has a shorter shelf life than other varieties of lettuce, but all types are highly perishable and should be consumed within one week. To reduce the risk of bacterial growth, refrigerate the lettuce within two hours. One cup of shredded red leaf lettuce has 4 calories and 1 gram of total carbohydrates. You'll get a little fiber, but only about 1 gram in a 1-cup serving.
Rich Source of Vitamin A
A large number of substances belong under the umbrella of vitamin A, but they're all categorized as retinoids or carotenoids, according to the Linus Pauling Institute. Retinoids are responsible for the health benefits associated with vitamin A, such as normal vision, healthy skin and immune support. Red leaf lettuce is a rich source of carotenoids, primarily beta-carotene. Your body converts beta-carotene into retinol, so it contributes to your daily vitamin A. You'll also get a smaller amount of the carotenoids lutein and zeaxanthin, which work as antioxidants in your eyes. One cup of red leaf lettuce contains 2,098 international units of vitamin A, or about 70 percent of the recommended dietary allowance of 3,000 international units.
Vitamin K for Bones and Blood
Your body uses vitamin K to form proteins that are best known for making blood clot. However, these vitamin K-dependent proteins fill other essential roles. They help maintain bone density by regulating the movement of calcium into your bones. Other proteins made from vitamin K inhibit the build-up of minerals in your blood vessels, which may help prevent hardening of the arteries, according to a review published in the January 2013 issue of "Trends in Molecular Science." You'll get 40 micrograms of vitamin K from eating 1 cup of shredded red leaf lettuce. This amount provides 44 percent of women's and 33 percent of men's recommended daily intake.
To qualify as a good source of any nutrient, foods must provide at least 10 percent of the recommended dietary allowance for that nutrient in one serving of the food, according to the U.S. Food and Drug Administration. While red leaf lettuce is not a good source of other nutrients, a 1-cup serving supplies a small amount of thiamin, riboflavin and vitamin B-6. The same portion also contains 0.34 milligrams of iron, or 2 percent of women's and 4 percent of men's recommended dietary allowance, according to the Institute of Medicine.
- U.S. Food and Drug Administration: Guidance for Industry: A Food Labeling Guide - Appendix A: Definitions of Nutrient Content Claims
- Centers for Disease Control and Prevention: Low-Energy-Dense Foods and Weight Management: Cutting Calories While Controlling Hunger
- Colorado State University Extension: Health Benefits and Safe Handling of Salad Greens
- USDA National Nutrient Database: Lettuce, Red Leaf, Raw
- Institute of Medicine: Dietary Reference Intakes (DRIs): Estimated Average Requirements
- Linus Pauling Institute: Vitamin A
- Bastyr University: Vitamin K for Bone Health
- Trends in Molecular Science: Vitamin K-Dependent Carboxylation of Matrix Gla-protein: A Crucial Switch to Control Ectopic Mineralization
- U.S. Food and Drug Administration: Guidance for Industry - A Food Labeling Guide: Appendix B - Additional Requirements for Nutrient Content Claims
- USDA National Nutrient Database: Lettuce, Green Leaf, Raw