A very interesting discussion on Radio New Zealand's This Way Up programme this weekend (19/04/2015) sparked some thinking about superfoods.
In the article, Mark Christensen of the Heritage Food Crops Research Trust expounded the value of heritage tomatoes, explaining that the lycopene found in red tomatoes could not be absorbed by humans unless it was cooked, but the variant in orange tomatoes was readily absorbed from raw foods. Lycopene is a 'phytochemical' (plant chemical) which is thought to have some potential health benefits.
We took a look at recent evidence for Lycopene, focussing on the areas mentioned in the radio article - Prostate and Heart Health.
We found that:
- There is good evidence that lycopene can be absorbed from the diet.
- Increased lycopene intake increases levels in the blood.
These two points are really important as many products that are touted as superfoods (such as turmeric) are not well absorbed, or are cleared by the liver and do not actually appear in the blood in any quantity. This means that tomatoes, or at least the lycopene in them passes the hurdle at which most superfoods fall.
- Reduces CRP (high levels are associated with higher risk of heart disease)
- Reduces several measures of oxidative stress. (Again, high levels are associated with higher risk of heart disease)
- Might slow the rate of increase in PSA in prostate cancer (though it is early days for these studies)
- Has an effect on the genes associated with the growth of prostate cancer.
So it is all looking quite promising for tomatoes so far - we can absorb the key ingredient from tomatoes and there is a plausible mechanism by which it may reduce heart disease.
Sadly, there are no quality clinical trials that have tested whether increasing tomato intake actually reduces heart disease or prostate cancer however, given that we know that higher intake of vegetables is associated with a lower risk of heart disease and given the evidence of plausible mechanism and some chemical evidence of benefit then it seems sensible to recommend tomatoes as a great addition to the diet.
So, should it be red or orange tomatoes?
The This Way Up article reported that the lycopene variant found in orange tomatoes was easier to absorb when raw than that in red tomatoes.
We were unable to find published evidence to support this assertion but it should be taken at face value. This sort of research is often unpublished or just very hard to find. Either way it makes no difference if tomatoes are cooked and there are no studies comparing the two colours directly in terms of dietary benefit.
Red tomatoes may however have higher lycopene content as this is associated with the red colour - lycopene content varies in commerce, some varieties having twice as much as others.
Overall, reds are probably better for cooking, orange may be better raw - there is, sadly, no good evidence to say whether or not orange is indeed the new red!
Don't forget that no superfood can neutralise the harm done by bad habits! Ketchup will not make a steak and cheese pie noticeably less harmful!