How Do Fat-Soluble Vitamins Differ From Water-Soluble Vitamins?

When it comes to supplements and medication, you’re often told to take something on an empty or full stomach. Why? Solubility. Fat-soluble vitamins should be taken with food, while water-soluble vitamins should be taken on an empty stomach. That's easy. But there's more.

These classifications are whittled down into two categories: fat-soluble and water-soluble. Vitamin and mineral solubility refers to how they get metabolized in your body, and plays an important role in determining effective and safe dosage amounts in your First & Foremost routine. The four fat-soluble vitamins (A, D, E, K) are absorbed by fat globules into your bloodstream, and the excess is stored in your liver or fatty tissue. Whereas the nine water soluble vitamins (the B vitamins and vitamin C) immediately dissolve in water and absorb into your tissue, excreting the excess in your urine. In this article, we’ll take a deeper dive into the differences between these two categories of vitamins. 

Fat-Soluble Vitamins

As we mentioned, vitamins A, D, E and K are fat-soluble, and they play integral roles in a multitude of physiological processes such as vision, bone health, immune function, and coagulation. As their name suggests, fat-soluble vitamins dissolve in fat globules that carry them throughout your bloodstream. However, before entering your bloodstream they must pass through the lymphatic system as part of a chylomicron. Because they are stored in your liver, adipose and cell membranes until needed, these nutrients do not get excreted once digested. The amount stored varies widely on the type of fat-soluble vitamin. This is something we kept in mind when formulating our dayparted program and quantifying your daily RDA, as it is possible to have a build-up of fat-soluble vitamins in your system and that is not necessarily a good thing. 

In our dayparted program, we provide vitamin E in the morning, vitamin K in the afternoon, A and D in the evening — because we’re not just dealing with solubility but several other factors that may affect absorption. And if you’re thinking about your diet, it’s helpful to know that you can find fat-soluble vitamins in foods with high-fat content, such as: egg yolks, liver, beef, tuna, salmon, fatty fish, and dairy products. 

Water-Soluble Vitamins

The water-soluble vitamins are B vitamins (folate, thiamine, riboflavin, niacin, pantothenic acid, biotin, vitamin B6, and vitamin B12) and vitamin C, and your body processes these vitamins differently than fat-soluble ones. They have varying roles in the body, often as coenzymes in a range of metabolic pathways. Water-soluble vitamins are absorbed directly into the bloodstream upon ingestion, as they can circulate freely within the water-filled compartments of the body.

The kidneys monitor the blood flowing through them, removing any excess in your urine (hence the phrase “expensive pee”). It is possible that taking too many of these vitamins at once can overwhelm the system and put strain on your kidneys, even putting predisposed individuals at risk of developing kidney stones. Because water-soluble vitamins are either used immediately or excreted quickly, it’s important to consistently eat nutrient-dense foods and maintain a supplement routine to fill the gaps in your diet. 

Water-soluble vitamins are easy to get from a balanced diet, but it should be noted that B12 is only found in substantial amounts in animal-sourced foods, so be mindful if you have dietary restrictions. We provide B vitamins and vitamin C in the evening occasion — you take them before bed, on an empty stomach, giving your body ample time overnight to digest and benefit from the nutrient content.

Our Dayparted Program 

Solubility is just one of four factors that affect bioavailability. When creating our day-parted program, we’ve kept that in mind along with complementary nutrients, conflicting nutrients, and form and chemistry. Therefore, when it comes to solubility and planning out the best time and way for you to get the most out of your nutrients, we've thoughtfully grouped fat-soluble and water-soluble vitamins for optimal absorption.