Salad Dressing Study: The Amount of Fat Matters More Than the Type
A salad dressing with some fat in it lets your body absorb more of the carotenoids in the vegetables, and a new Purdue University study adds that the amount of fat matters more than the type. It is being reported this week as proof that olive oil is the best dressing, but the study did not test olive oil at all. Here is what it actually did, what it found, and how to dress a salad sensibly.
What the study did
Researchers led by a team at Purdue University gave 29 healthy volunteers the same vegetable salad on different occasions, dressed with 3, 8 or 20 grams of fat. The fat came from one of three sources: canola oil, which is rich in monounsaturated fat, soybean oil, which is mostly polyunsaturated, or butter, which is mostly saturated. Over the next ten hours the team measured how much of the salad’s carotenoids, such as beta-carotene, lutein and lycopene, turned up in the blood fractions that carry newly absorbed fat.
The paper, in the June issue of Molecular Nutrition and Food Research, reports two things. First, 20 grams of fat led to higher absorption than 3 or 8 grams for almost every carotenoid measured. Second, the source of the fat mattered less than the amount. Canola oil showed a trend toward better absorption of lutein and alpha-carotene than butter, but the difference fell short of statistical significance.
| Question | What the paper reports |
|---|---|
| Does more fat help? | Yes: 20 g beat 3 g and 8 g for nearly all carotenoids |
| Does the type of fat matter? | Less than the amount |
| Monounsaturated vs saturated | Canola trended better than butter for two carotenoids, not significant |
| Was olive oil tested? | No; canola was the monounsaturated fat |
How it is being reported
Coverage this week has focused on the idea that monounsaturated fat gives the same carotenoid absorption at 3 grams as at 20, so a small amount of an olive oil type of fat is all you need. Olive Oil Times, to its credit, pointed out that the monounsaturated oil used was canola, while noting that olive oil is even richer in monounsaturated fat. The paper’s own summary is more cautious than the headlines: while both the amount and the source of fat affect how much you absorb, the amount appears to have the stronger effect.
What it means in practice
- Do not skip the fat entirely. Earlier research found that carotenoids are absorbed much better when a salad contains some fat.
- A reasonable amount beats a token drizzle for absorption, though calories count too; a tablespoon of oil is about 14 grams.
- Olive oil is a good choice for other reasons. It is mostly monounsaturated fat, and the virgin grades bring flavor and polyphenols of their own, but this study cannot tell you it beats other oils for carotenoids.
- Tomatoes and oil belong together. Southern European cooking has long paired them, and absorption of lycopene is one good reason.
Olive oil marketing will quote any study with the word monounsaturated in it, even one that used canola. Before sharing a health headline, check two things in the abstract: which oil was actually tested, and whether the difference was statistically significant. Here the answers were canola, and not quite.
This is general information, not medical or dietary advice. If you are managing your weight, cholesterol or a medical condition, ask your doctor or a registered dietitian how much fat suits you.
For salads and dishes built on oil and vegetables, see Salmorejo: Córdoba’s Cold Tomato Cream, Emulsified in Oil and Panzanella: Tuscany’s Bread Salad, Built on Oil. On the nutrition side, Olive Oil Good For More Than The Monounsaturated Fats.
Sources
- PubMed: Goltz et al., Meal triacylglycerol profile modulates postprandial absorption of carotenoids in humans, Mol Nutr Food Res 2012
- Olive Oil Times: Dress Your Salad in Olive Oil to Get the Most Nutrients