In a recent peer-reviewed paper published in the American Journal of Clinical Nutrition, White and colleagues (2017) wanted to determine if there's a dose-dependent effect of soybean oil in salad dressing on nutrient bio-availability from vegetables.
What they did:
- gave 12 women 5-vegetable salads containing 0, 2, 4, 8, 32 grams of soybean oil
- took blood samples at different time points
- the nutrients of interest were: alpha and beta carotene, lutein and lycopene
- they looked at the area under the curve (AUC) for different circulating chylomicrons
As per the researchers:
"Absorption of all carotenoids and fat-soluble vitamins was highest with 32 g oil (P < 0.002). For 32 g oil, the interindividual rank order of the chylomicron AUCs was consistent across the carotenoids an d fat-soluble vitamins (P < 0.0001)." [source]
According to White, better nutrient absorption provides health benefits. Simply put, in White's words, doubling the amount of salad dressing doubles the absorption of nutrients.
Now, before you add ridiculous amounts of oil and fat to your salad dressing, you should know that funding for this study was provided by Unilever (a food company). Unilever formulated the dressing and also hired the consultant who did part of the statistics of the research.
To be honest, I did not carefully read the materials and methods of this study, but I'd be careful in driving conclusions and practical take away messages, not only because of the funding (and if you read the study, you might see a little nudging in favor of more oil and fat consumption with vegetables), but also because of the small sample (n=12) and some important variables from the participants' lives which have not been taken into consideration.
Here's something to consider: A large salad of non-starchy vegetables could be as little as 50-60 calories and could go to 150-200 kcals or even more, depending on the vegetables. This is a lot of volume (plenty of vitamins, minerals, and micronutrients) and very few calories.
A salad dressing made of olive oil (4 grams), salt, pepper, and vinegar would add 36-40 calories, which is reasonable. Now, 32 grams of oil would add about 290 calories more to the salad, twice as much as the vegetables), and that is not reasonable if you ask me, even if this study is funded or not funded.
So, shall we consider this just another case of bad science? Judge that for yourself.
If you'd like to scrutinize this study further, you can read it entirely:
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Cristi Vlad Self-Experimenter and Author