Each 2-ounce serving of roast beef has approximately 70 calories. Usually 2 ounces is about two regular slices, or four thinly-sliced pieces, although if you're carefully keeping tabs on your calories, weigh your slices first to be sure. More than half of the calories in roast beef lunch meat are from protein, while the remaining amount comes mainly from fat and a few carbohydrates.
Most of the calories in roast beef come from protein. The protein content varies from roughly 9 to 10 grams in a 2-ounce portion, accounting for 36 to 40 calories. That same 2-ounce portion gives you 2 to 3 grams of fat, or 18 to 27 calories from fat. Like many processed deli meats, roast beef lunch meat does have carbohydrates. You'll only get a trace amount though, usually less than 2 grams of carbohydrates per 2-ounce serving, contributing fewer than 8 calories.