The term ‘superfood’
has become a popular buzzword in the language of food and health. However,
there is no technical definition of the word and the scientific evidence for
the health effects of these foods — while often positive — does not necessarily
apply to real diets. A diet based on a variety of nutritious foods, including
plenty of fruits and vegetables, remains the best way to ensure a balanced
nutrient intake for optimal health.
The origin of the superfood
The concept of the superfood is a popular one when it comes to food and health.
The media is full of reports of ultra-healthy foods, from blueberries and
beetroot to cocoa and salmon. These reports claim to reflect the latest
scientific evidence, and assure us that eating these foods will give our bodies
the health kick they need to stave off illness and aging. But is there any
truth to such reports?
The current attention on superfoods has likely been encouraged by a growing
public interest in food and health, particularly in the developed world.1
While the use of the term has been recorded as far back as the beginning of the
20th century, it has only recently become popular in mainstream language.2
A simple internet search for the word, superfood, reveals close to 10 million
results — predominantly from health and nutrition blogs, online newspapers and
magazines, and providers of nutritional supplements.
Despite its ubiquity in the media, however, there is no official or legal
definition of a superfood. The Oxford English dictionary, for example,
describes a superfood as “a nutrient-rich food considered to be especially
beneficial for health and well-being”, while the Merriam-Webster dictionary
omits any reference to health and defines it as “a super nutrient-dense food,
loaded with vitamins, minerals, fibre, antioxidants, and/or phytonutrients”.3,4
Generally speaking, superfoods refer to foods — especially fruits and
vegetables — whose nutrient content confers a health benefit above that of
other foods.
What is the evidence?
In order to distinguish the truth from the hype, it is important to look
carefully at the scientific evidence behind the media’s superfood claims.
Blueberries are one of the more popular and well-known superfoods, and have
been studied frequently by scientists curious about their health properties.
The berries’ high concentrations of a group of antioxidant plant compounds,
especially those called anthocyanins, have been reported to inhibit the growth
of cancerous human colon cells, as well as kill them off.5
Blueberries are also rich in other antioxidants, which have been shown to
prevent and reverse age-related memory decline in rats.6
Antioxidants are molecules which protect the cells in the body from harmful
free radicals. These free radicals come from sources such as cigarette smoke
and alcohol, and are also produced naturally in the body during metabolism. Too
many free radicals in the body can result in oxidative stress which, in turn,
causes cell damage that can lead to age-related diseases like cancer, diabetes,
and heart disease.7
Other fruits which have received superfood status include açaí berries and
pomegranates. The fruit pulp of açaí berries has been shown to have potent
antioxidant properties, although any potential health benefits of this have yet
to be confirmed in humans.8,9 Studies on pomegranate juice have
suggested that it can lower blood pressure in the short-term, as well as reduce
oxidative stress, in healthy people.10,11 These are both significant
risk factors for heart disease.
Like pomegranate juice, beetroot has been proposed as a heart-healthy
superfood. Its high levels of nitrate are claimed to be converted by the body
into nitric oxide which, among other functions, has been shown to lower blood
pressure and the tendency for blood clotting in humans.12 Cocoa has
similarly been claimed to cut the risk of heart disease by lowering blood
pressure and increasing the elasticity of blood vessels. This is thought to be
due to cocoa’s high content of compounds called flavonoids.13,14 Finally,
salmon has frequently made it onto superfood lists amid growing evidence that
the omega-3 fatty acids in salmon and other oily fish may prevent heart
problems in people with a high cardiovascular risk, as well as alleviate joint
pain experienced by patients with rheumatoid arthritis.15-17
Looking closer
These are just a handful of the many studies that have looked at the health
properties of foods. At first glance, they appear to lend weight to the
existence of certain superfoods — certainly, the nutrients in these foods have
been shown to have several health-promoting properties. But a closer look
reveals the difficulty in applying the results of these studies to real diets.
This is because the conditions under which foods are studied in the lab are
often very different to the way these foods are normally consumed by people in
their everyday lives.
One major characteristic of research in this area is that very high levels of
nutrients tend to be used. These are usually not realistically attainable in
the context of a normal diet. On top of this, the physiological effects of many
of these foods are often short-term.12,13 This means people would
need to consume them often in order to reap their health benefits. This could
be counter-productive, especially for certain foods: frequently consuming cocoa
in the form of chocolate, for example, would boost intakes not only of cocoa’s
health-promoting flavonoids but also of other nutrients of which we are
recommended to consume less.
Perhaps an even greater consideration when looking at these studies is that
many of them tend to use either animal models such as rats, or in vitro
experiments using isolated batches of human cells. These types of studies are
useful for giving scientists an idea of what the health properties and
physiological mechanisms of certain food components could be, but there is no
guarantee that these components will have the same effects in people when
consumed in the diet. Investigating effects in humans is a complex task: our
diets, genes, and lifestyles vary from person to person, making it difficult to
study the impact of nutrients on health. This means that, in contrast to cell
culture and animal studies, a different approach is needed when exploring
effects in humans that ideally includes both intervention studies (where
researchers manipulate the diet to determine the effect of a food or nutrient)
and observational studies (where researchers observe the effects of natural
differences in people’s diets).
A final point to consider when looking at studies on the ‘healthfulness’ of
foods is that many researchers study foods in isolation. Given that people
normally consume combinations of foods, picking out a single one to study does
not reflect real human consumption. What’s more, there is evidence to suggest
that in some cases co-consumption of foods can actually increase the body’s
ability to absorb nutrients. The beta-carotene in carrots and spinach, for
instance, is more readily absorbed when eaten together with a source of fat such
as salad dressing.18 This hints at the merits of a diet based on a
variety of nutritious foods as opposed to a diet based solely on one or a
handful of superfoods.
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