Sardines

Sardines deliver 25g of protein per 100g along with calcium from edible bones, vitamin D, and omega-3s, all with virtually zero mercury contamination. They are among the most nutrient-dense protein sources per calorie, providing 350mg of calcium per serving—three times more than grass-fed beef. Their sustainability rating is among the best of any seafood, outperforming lamb in terms of carbon footprint by a factor of 10.