Vitamin K Absorption and Fat: A Closer Look

Dietary fat is important for the absorption of all fat-soluble vitamins partly because it helps dissolve the vitamins and partly because it helps stimulate the machinery involved in fat digestion, such as bile acids and lipases. Studies have generally suggested the following rule: the more fat you eat, the more fat-soluble vitamins you absorb. For example, 28 grams of fat allows better absorption of carotenoids from a salad than 6 grams of fat (Brown, 2004), and 30 grams of fat allows better absorption of vitamin E from a supplement than 11 grams of fat (Bruno, 2006). Studies have also shown that oils lower in polyunsaturated fatty acids (PUFAs) promote better absorption of fat-soluble vitamins than high-PUFA oils. For example, beef tallow allows better absorption of beta-carotene from a standardized test meal than safflower oil (Hu, 2000).

These rules appear to apply to vitamin K just the same. For example, 35 grams of fat allows better absorption of MK-4 than 20 grams of fat (Uematsu, 1996), and more K₁ is absorbed from spinach with 25 grams of butter than without butter (Gijsbers, 1996). More K₁ was absorbed from a “cosmopolitan” meal or an “animal-oriented” meal than from a “convenience meal,” with one possible explanation being the two-fold greater PUFA content of the convenience meal (Jones, 2009).

None of these studies showed a ceiling to the fat effect, and none of them tested more than 35 grams of fat. So, there may not be any ceiling to the effect. What we can say with confidence is that 30-35 grams of fat will provide for better absorption than lower amounts. Even still, absorption will probably never reach 0% or 100%, and for any given percent absorption one can always absorb a greater total amount of a vitamin by consuming more of it. Therefore, there is no sense in chasing after complete absorption and there is no intrinsic danger of a low-fat diet. If you have a good reason to eat less than 35 grams of fat per meal, it just becomes more important to spend the fat you do eat wisely by allocating it to K₂-rich foods. It is fine to be flexible about fat intake, but it is important to be aware that any given amount of K₂ in the diet will provide more nutrition to our bodies if consumed with a good dose of healthy fat.