To Your Health

Q. Are nutrients in a pill absorbed as well as nutrients in food?

A. Nutrient absorption can get tricky. Usually it is more than simply a molecule crossing from the intestinal tract into the body where it will be used. This does happen, and is known as "passive" absorption, but most often nutrient absorption requires energy and is tightly controlled by the gut. Many factors influence the end results of eating, and these factors are still not well understood. What we do understand leaves us awed.

The vitamins and minerals in the best supplement products, especially when taken at a meal, dissolve easily and mix with the food. Synthetic vitamins that are "bioidentical" to vitamins in food will be absorbed and utilized in the same way as the vitamins provided by the food. The energy from the food and the enzymes contained in digestive juices work together to facilitate absorption of the nutrients both from the food and those supplied in pill form.

The most obvious limitation to nutrient absorption from either food or a pill is size. Vitamin B-12, the largest of the B-vitamins, even requires a special transporter called "intrinsic factor" in order to make it into the body. In the absence of this carrier, less than one-thousandth of the vitamin B-12 consumed would be absorbed. An individual whose body does not make intrinsic factor simply cannot obtain enough vitamin B-12 from food to survive and must rely on either shots or very high-dose vitamin B-12 oral supplements.

The acid/base (pH) balance also must be correct for the best absorption, especially for minerals. The "correct" pH changes three times as food passes from mouth to stomach to small intestine to large intestine. At each stage the body devotes considerable energy to adjusting the pH for optimum efficiency. Age is a major factor in mineral absorption partly because as we age, we lose this control over pH. Mineral supplements that do not take into account the effect of pH on absorption will not be as effective as we could wish.

Although it doesn't sound reasonable, rapid absorption is not necessarily the best. Slowing the rate of absorption by increasing the "transit time" (the time between ingestion and excretion of food) seems to allow time for the body to keep control over what is happening. This may be one reason that taking food supplements with a meal generally does better than taking them on an empty stomach.

Too-rapid transit time is associated with diarrhea, and a transit time less than 12 hours simply does not allow enough time for ideal absorption. At the opposite extreme, a transit time of two to three days, quite common among Americans eating a low-fiber diet, allows bacterial toxins to damage the lining of the intestinal tract and reduce its ability to absorb nutrients. Transit time can be adjusted by changing fiber intake, and the right amount of fiber is the amount that yields a transit time of slightly less than 24 hours.

As usual, there are exceptions to these rules. One example is folic acid. In food it is combined with a molecule of glutamic acid that must be removed before it can be easily absorbed. Folic acid in pills already has that glutamic acid molecule removed and so is slightly better absorbed than folic acid from food.

As we mature, our body's ability to absorb nutrients decreases by about 10% per decade of life. It makes good sense to apply all our nutritional knowledge to the goal of keeping our digestive system functioning well.