Beef Flank Steak Nutrition Calculator — Calories & Nutrition per Serving

Broiled flank steak (lean only) delivers 192 kcal per 100g with 27.7g protein — a protein-to-calorie ratio of 14.4g per 100 kcal ^[1]. Only tenderloin (14.5g/100 kcal) matches this efficiency among beef steaks, at roughly double the retail price.

The fat content of 8.2g per 100g places flank among the leanest steaks — comparable to top round (6.9g) and considerably below ribeye (21.8g). The trim difference between lean and lean + fat is only 9 kcal per 100g (192 → 201) because flank steak has minimal external fat — it's essentially a single, thin, flat muscle with almost no separable fat ^[1].

Proteomic analysis of beef tenderloin and flank steak has confirmed that flank steak's distinct muscle fiber orientation (long, coarse fibers running the length of the cut) contributes to a slightly different amino acid profile, with higher concentrations of structural proteins like collagen and elastin compared to tenderloin's finer-grained muscle ^[2].

Broiled flank steak provides 370mg potassium per 100g — the single highest potassium reading among all beef steaks in the USDA database ^[1]. For context: sirloin delivers 368mg, round delivers 342mg, and ribeye delivers 282mg. A 6-oz flank steak provides 629mg potassium (13% DV).

Flank steak is a large, flat muscle from the abdominal wall (the obliquus abdominis) that performs constant postural work. This continuous activity promotes higher concentrations of potassium — the electrolyte essential for muscle contraction and cellular fluid balance ^[1].

Nutritional analysis from grass-fed beef sources has confirmed that flank steak's potassium advantage holds across both conventional and grass-fed production systems, with grass-fed flank averaging 375–385mg per 100g raw ^[3].

Flank steak has long, visible muscle fibers running its length. Slicing against the grain (perpendicular to the fibers) shortens each fiber to the width of the slice, making every piece tender. Slicing with the grain leaves long, intact fibers that are chewy and difficult to eat ^[1].

The nutrition per gram is identical regardless of slicing direction — a 100g serving contains 192 kcal and 27.7g protein whether cut into thin bias slices, thick planks, or stir-fry strips. However, slicing direction affects portion perception: thin bias-cut slices spread across a plate look like a larger serving than a single thick piece of the same weight ^[1].

For stir-fry tracking: slice flank steak ¼-inch thick against the grain before cooking. The high surface-area-to-mass ratio means stir-fry strips absorb more oil and sauce per gram of meat than whole steaks — which is why the stir-fry variant shows 215 kcal vs 192 kcal per 100g (the additional ~23 kcal comes from cooking oil absorption) ^[2].

"London Broil" is a cooking method (marinate, broil, slice thin), not a specific cut — but American grocery stores often label flank steak as 'London Broil' interchangeably. In French and European butchery, the same muscle is called bavette (from bavette d'aloyau) ^[1].

Regardless of the label, the nutritional profile is identical: 192 kcal, 27.7g protein, 8.2g fat per 100g broiled lean. If you see 'London Broil' at the supermarket, you can use flank steak values for tracking. Some butchers also label top round as London Broil — round is slightly leaner (165 kcal, 6.9g fat/100g) with less flavor ^[1].

The key identification: true flank steak is flat, wide, and about ¾–1 inch thick with clearly visible long grain lines. Top round is thicker, more uniformly shaped, and has a finer grain. If the London Broil label at your store looks thick and round-shaped, it's likely top round — use round values instead ^[3].

Raw flank steak has 155 kcal per 100g. Broiling raises it to 192 kcal (24% increase from moisture loss). Grilling to 197 kcal (slightly more surface dehydration). Stir-frying to 215 kcal (39% increase due to oil absorption in thin strips) ^[1].

The moisture loss during cooking is approximately 25–30% for broiling and grilling. A 680g whole raw flank steak yields approximately 475–510g cooked. For stir-fry with thinner cuts and higher heat, yield drops further to approximately 430–460g from the same starting weight ^[1].

For taco or fajita night: a typical flank steak taco filling is about 60g of sliced grilled meat (approximately 118 kcal, 16.8g protein) plus tortilla (about 150 kcal) and toppings. Log the meat weight separately from the assembly to keep tracking accurate ^[2].