Phytochemicals in foods: some examples
In this activity we offered a quick overview of what micro and macronutrients are, as food items sold with the “superfood” label often contain high amounts of some essential nutrient.
We already said there is another element often linked with superfoods, and it is the presence of some “healthy” molecule. It can be the case of molecules contained in herbs and spices, like garlic or turmeric.
In many cases, however, the phytochemicals found in superfoods (like in “regular” fruits, seeds and vegetables) belong to the class of polyphenols. You might already be familiar with this term, as polyphenols are contained in several healthy foods, such as olive oil. They are not only part of the reasons why olive oil is considered healthy, but are also partially responsible for its flavor.
Polyphenols are a very large class of molecules, and they include flavonoids, the subject of the third week of this course. Some polyphenolic molecules have been the subject of much attention - it is the case, for instance, of resveratrol, who was widely studied because of its possible association with the “French paradox” of a low incidence of cardiovascular disease despite a high consumption of saturated fats.
Foods rich in this molecule include grapes skin (and therefore red wine, its connection with the French Paradox), as well as in superfoods like some berries (bilberries, mulberries and blueberries) and in peanuts.
Does resveratrol have a beneficial effect on our health?
The answer is uncertain: on simple animal models (such as worms, yeasts, and fruit flies) resveratrol is linked to an increased lifespan, but we don’t know yet if these results generalize to humans. The same is true for the anti-cancer properties of resveratrol: while the results on cell cultures are promising, there is no conclusive proof of its effectiveness in humans.
Unfortunately, the vast majority of studies on resveratrol were conducted in cell cultures or animals, and not in humans. While there is evidence that even a single elevated dose of resveratrol can affect physiological parameters such as arterial pressure and brain blood flow, and despite the fact that studies on the health benefits of drinking a moderate red wine have been going on for decades, we do not know yet if this molecule can be a safe and effective supplement to our diet, able to improve our health.
Many vegetables also contain phytochemicals with a possibly positive health effect, but not related to polyphenols. An example comes from carotenoids, a family of plant pigments that is found both in superfoods such as kale and in very traditional foods, such as tomatoes and (of course) carrots. Some carotenoids can be converted into vitamin A into our body, while others can’t.
Lutein and zeaxantin belong to this latter category, but they are both present in the retina, where they absorb blue light and protect crucial structures from UV and oxidative damage.
These molecules are found in one of the most famous superfoods, kale. As we will see in the next week, kale shares many of its properties with less glamorous foods, such as spinach. In fact, both kale and spinaches are good sources of lutein and zeaxantin, as are other green leafed vegetables.
Are these molecules really improving our health?
Health benefits of foods are often assessed through observational studies: groups of people are observed for long periods of times, and their diet and/or biochemical markers recorded, along with the incidence of specific illnesses, or general mortality.
Sometimes it is hard to separate the effect of a specific molecule from the other phytochemicals contained in these foods. For instance, a study investigated the relationship between the intake of lycopene, a carotenoid mostly found in tomatoes, and cardiovascular diseases, observing the diet and recording the health status of more of 5000 people, for 10 years.
They did find that lycopene intake was inversely associated with CVD (that is, more lycopene was associated with less frequent cardiovascular disease), but as the author themselves say,
“additional research is needed to determine whether lycopene or other components of tomatoes, the major dietary source of lycopene, are responsible for the observed association.”
Ultimately, we eat foods, and not isolated chemical compounds. Moving from the results obtained on a molecule to dietary advice is not an easy task, and is not automatic.