When I eat salads, should I skip the dressing? What about cooked vegetables? Are they healthier without fat?

Absolutely not! Fat-free dressings deprive you of absorbing carotenoids—the red, yellow and orange pigments in fruits and vegetables that act as antioxidants, preventing the free radical damage that leads to aging and chronic disease.

A study published in the August 2004 issue of the American Journal of Clinical Nutrition demonstrates that adding a little fat to your salads and cooked vegetables can make a big difference in the amount of these protective compounds you absorb.

In this study, subjects each ate 3 salads that differed only in the amount of fat in the salad dressing. After eating each salad, the subjects' blood levels of carotenoids (alpha-carotene, beta-carotene, and lycopene) were checked hourly for 12 hours with the following results:

  • Essentially no carotenoids were absorbed when the salad was eaten with fat-free dressing.
  • Reduced fat dressing resulted in minimal carotenoid absorption.
  • Eating the salad with full fat dressing caused subjects' blood levels of carotenoids to rise substantially.

Why is this so? Because carotenoids are fat-soluble plant pigments, and being fat, rather than water-soluble, they cannot be absorbed unless fat is present.

When fats are eaten, the body responds by squirting bile (which is made in the liver and stored in the gallbladder), into the small intestine. Bile breaks up the fat into tiny globules called micelles that transfer their contents to the intestinal wall, where the nutrients are packaged into chylomicrons—a form in which they can be absorbed into the lymphatic system, sent to the liver, and then into the bloodstream.

So, no fat = no bile secretion = no carotenoid absorption.

But you don't need lots of fat—studies suggest that as little as 3-5 grams (approximately 2 teaspoons) can facilitate carotenoid absorption.

Carotenoids' fat-soluble nature is also the reason why studies have shown that the lycopene in tomatoes is absorbed in highest amounts from cooked tomato products that contain a little olive oil. In products like tomato sauce or paste, cooking has helped break down cell walls, liberating lycopene, but it is the addition of oil that ensures bile will be secreted into the intestines, assuring the carotenoid's incorporation into micelles and absorption.

The same holds true for other cooked vegetables as well. To get the most benefit from the cooked vegetables you eat, cook lightly without fat (heat damages fats producing free radicals), then add a little fat before serving (to ensure carotenoid absorption):

  • Dress salads and cooked vegetables with a tablespoon of extra virgin olive oil*, freshly squeezed lemon juice or balsamic vinegar, and your favorite herbs and spices.
  • Toss in a handful of raw or lightly roasted nuts or seeds (roasting at high temperatures damages nuts' delicate fats).
  • Add several slices of avocado or an ounce of cheese (shredded organic mozzarella or some crumbled feta are good choices since these naturally low-fat cheese will provide enough to put the carotenoids in your bloodstream, but not so much that you'll find yourself putting on fat.)
  • Cutting calories? For a delicious raw vegetable dip that will supply the fat you need for carotenoid absorption, plus calcium, for up to half the calories of oil-based dressings, mix ¼ cup full-fat plain organic yogurt with your favorite herbs and spices. For a richer dip, add a teaspoon of olive oil*.
  • Remember organic is especially important in full fat dairy products since pesticides and other toxins concentrate in animal fats.

*You can also use flaxseed oil as an alternative to olive oil.

How to Cook for Maximal Carotenoid Absorption

A study published in March 2000 issue of the Journal of Nutrition notes that “Processing, such as mechanical homogenization or heat treatment, has the potential to enhance the bioavailability of carotenoids from vegetables (from 18% to a sixfold increase).”

The key word here is “potential”—overcooking destroys phytonutrients, so be sure to steam lightly or use the Healthy Sauté technique to maximize carotenoid retention as well as availability. If you're using one of the World’s Healthiest Foods’ wonderful recipes, just follow the directions—we have done all the work to maximize nutrient retention and flavor for you.

References

Brown MJ, Ferruzzi MG, Nguyen ML, Cooper DA, Eldridge AL, Schwartz SJ, White WS. Carotenoid bioavailability is higher from salads ingested with full-fat than with fat-reduced salad dressings as measured with electrochemical detection. Am J Clin Nutr. 2004 Aug;80(2):396-403.

Gartner C, Stahl W, Sies H. Lycopene is more bioavailable from tomato paste than from fresh tomatoes. J Clin Nutr. 97 Jul;66(1):116-22.

Parker RS, Swanson JE, You CS, Edwards AJ, Huang T. Bioavailability of carotenoids in human subjects. Proc Nutr Soc. 1999 Feb;58(1):155-62.

Ribaya-Mercado JD. Influence of dietary fat on beta-carotene absorption and bioconversion into vitamin A. Nutr Rev. 2002 Apr;60(4):104-10.

Roodenburg AJ, Leenen R, van het Hof KH, Weststrate JA, Tijburg LB. Amount of fat in the diet affects bioavailability of lutein esters but not of alpha-carotene, beta-carotene, and vitamin E in humans. Am J Clin Nutr. 2000 May;71(5):1187-93.

Traber MG. The bioavailability bugaboo. Am J Clin Nutr. 2000 May;71(5):1029-30.

Tyssandier V, Cardinault N, Caris-Veyrat C, Amiot MJ, Grolier P, Bouteloup C, Azais-Braesco V, Borel P. Vegetable-borne lutein, lycopene, and beta-carotene compete for incorporation into chylomicrons, with no adverse effect on the medium-term (3-wk) plasma status of carotenoids in humans. Am J Clin Nutr. 2002 Mar;75(3):526-34.

Tyssandier V, Reboul E, Dumas JF, Bouteloup-Demange C, Armand M, Marcand J, Sallas M, Borel P. Processing of vegetable-borne carotenoids in the human stomach and duodenum. Am J Physiol Gastrointest Liver Physiol. 2003 Jun;284(6):G913-23.

van Het Hof KH, West CE, Weststrate JA, Hautvast JG. Dietary factors that affect the bioavailability of carotenoids. J Nutr. 2000 Mar;130(3):503-6.

This page was updated on: 2005-08-24 17:51:49
© 2002 The George Mateljan Foundation