If you’ve been alive anytime  in the last… centuries,   you haven’t been able to avoid  the concept of diet programs.

Since 1864, when an early fad diet sang  the praises of the low-carb lifestyle,   we’ve been inundated with diet  books, ads, and storefronts. A lot of these diets come and go, but  some of them have real sticking power,   especially when they’re reflective  of established nutritional patterns.

One diet you’ve probably heard  of is the Mediterranean diet. And one of the reasons you may have  heard of it is that it actually works. Like, weirdly well.

And in some ways, it doesn’t seem like it  should work. So what does the research say   about this pattern of food intake, and how  do we even go about researching this at all? Diet advice should be taken with a grain of salt,   but maybe this one could be  taken with a dash of olive oil. [♪ INTRO] Real quick, this video is about diet stuff,  including things like calorie restriction.

If that’s not a cool topic for you, we  don’t mind if you want to skip this one. Officially speaking, the Mediterranean  diet describes the typical pattern of   eating in Crete and southern Greece around 1960. Similar diets come from other  areas of the Mediterranean Basin,   including southern Europe,  northern Africa, and western Asia.

In other words, areas that grow a lot of olives. Those olives are critical,  not because of martinis,   but because one of the notable features of  the Mediterranean diet is that olive oil   is the primary source of fat,  and it is not used sparingly. In fact, up to 40% of the calories for  people who eat this way come from fat.

For a long time, the prevailing wisdom was  that that much fat was not a good thing,   but as we’ll see, this diet proves otherwise. The diet also includes a lot of fruit, vegetables,  nuts, breads, and other plants, low or moderate   amounts of fish, poultry, dairy, and red wine,  and low amounts of red meat and processed sugars. So to be clear, the Mediterranean  diet is not a fad diet, it’s just... the diet of Mediterraneans.

While yes, there are tons of contemporary  cookbooks with attractive influencer-types   on the cover, the dietary pattern has  actually been officially recognized   by UNESCO as a cultural heritage  connected to its geographical origin. The first epidemiological study of  the diet began in 1958, collecting   decades of research on middle-aged  male residents of seven countries. In the years since, it’s become one of the most  well-studied dietary patterns in the world.

But it’s tough to study the impacts of a diet. In an ideal world, we’d do a  randomized controlled trial,   where large numbers of participants are  sorted into groups, one group follows the   Mediterranean diet for decades,  and one group eats other stuff. But that’s not really possible with something  as comprehensive as a dietary pattern.

Getting tens of thousands of people to change   their entire diets for decades for  a scientific study is a huge ask. But randomized controlled trials are  the gold standard in health research,   and it’s not like you can’t do them at all. Where it makes sense is on shorter timeframes  to study what are called surrogate markers.

These are intermediate health outcomes that  relate to a specific diagnosis or endpoint,   which you can use to approximate  how that endpoint is going. So, for example, you can use blood  pressure or cholesterol as a surrogate   marker for coronary heart disease, or serum  estradiol for postmenopausal breast cancer. And it’s a lot easier to keep track of  what somebody eats for a year and see   how that affects their LDL cholesterol than  to ask them to change their diet for decades   to see whether they eventually  develop coronary heart disease.

Researchers complement these shorter randomized  controlled trials with prospective cohort studies. In this type of study, researchers follow   groups of people before any of the  outcomes they’re studying occur. So if you wanted to study whether  the Mediterranean diet affects the   development of heart disease, you wouldn’t  select participants who already had heart   disease to see how following the  Mediterranean diet affected it.

You’d select participants, track what  they eat over long periods of time,   and follow who gets heart disease at what point. Mediterranean diet studies typically  aren’t separated into simple,   “yes this person follows the  diet, no this person doesn’t”. Instead, they use a score that assigns  points to different aspects of the diet,   like a D&D character sheet.

Participants get a rating  on 9 different components. For example: do they eat more  fruit and nuts than most people? Do they eat more vegetables, do they eat less  meat, do they drink moderate amounts of alcohol?

In these types of prospective studies,  that allows researchers to see when   participants follow Mediterranean  eating patterns more or less closely. If people are more likely to develop heart  disease when they’re eating less like the diet,   that can suggest that the diet is related. By combining results from these two types of   studies, researchers can make a  stronger claim about causality.

Basically, you have indirect evidence  from the observational study that   following the diet more closely over  the long term reduces heart disease. And you have direct evidence from the   interventional studies that the  diet lowers LDL cholesterol. Put these together, and scientists can make a   pretty compelling case that the Mediterranean  diet lowers the risk of heart disease.

And while the actual research methods are  a little complicated, they tell us a lot. A 2021 comprehensive review looked at studies  of the impact of the Mediterranean diet on   seven different health outcomes and rated the  strength of the research on a zero to four scale. Zero represented no evidence of a link,  and 4 represented convincing evidence of   a link backed up by multiple lines of  evidence of the types we’ve discussed.

And none of the health outcomes they looked at  scored below a two, which means there was at   least suggestive evidence of the Mediterranean  diet having an impact on every single one. We’ll get into the specifics in a moment,   but first, all science needs  funding, so here’s a quick break. Introducing the new Brilliant!

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You can upgrade to Premium to unlock all courses. And right now, SciShow viewers can save 20% off  an annual subscription at brilliant.org/scishow. The strongest evidence category starts off with  cardiovascular disease, where cohort studies   show that higher Mediterranean diet scores  are associated with lower risk of coronary   heart disease, reduced risk of stroke, and fewer  cases of and deaths from cardiovascular disease.

The Mediterranean diet also lowered blood  pressure, blood lipids like cholesterol,   and markers of inflammation  in intervention studies,   giving it a big thumbs up for its  ability to improve our heart health. Diabetes is also in this category, with  cohort studies showing that people who   follow a Mediterranean diet have a lower risk  of type 2 diabetes, and intervention studies   showing that type 2 diabetes patients that  follow the diet have better glycemic control. Rounding out the convincing evidence is metabolic  syndrome, which makes sense because metabolic   syndrome relates to risk factors for both  cardiovascular disease and type 2 diabetes.

In prospective studies,   people who eat the Mediterranean way  have lower risk of metabolic syndrome,   and in intervention studies it’s more likely to  go into remission when people follow the diet. That’s a really strong start  for the Mediterranean diet. In that same review of health impacts, the  “highly suggestive” category reflects health   outcomes with 3 or more observational  studies reporting a relationship with   the Mediterranean diet, with no  studies that clearly refute them.

Cognitive function fell into this category,  with adherence to the Mediterranean diet being   associated with lower risk of Alzheimer’s  disease and age-related cognitive decline. Cancer was also in this category. There’s evidence of a relationship between the  Mediterranean diet and lower risk of breast   cancer, as well as lower overall rates  of cancer incidence and cancer deaths.

Our final category are the health outcomes   where the evidence is suggestive that the  Mediterranean diet can make a difference. By suggestive, the researchers mean there  are one or two studies that support the link,   and no studies that clearly refute it. To start off, while overall cancer risk and  death were in the highly suggestive category,   most specific cancers fall here: specifically,   colorectal, head and neck, respiratory,  gastric, liver, and bladder cancer.

Overweight and obesity fall in this category, too. It may seem counterintuitive  because culturally speaking,   we tend to associate the concept  of “diets” with weight loss. We also tend to associate the idea  of weight loss diets with low-fat,   and this is far from a low-fat diet.

That’s why some doctors don’t recommend it as   often for weight loss as they  do for other health concerns. There is, however, compelling  evidence that the Mediterranean   diet doesn’t cause weight gain or  increases in waist circumference. And when it comes to losing weight and fat, there  is some evidence that the Mediterranean diet is   more effective than some other diets when people  are restricting how many calories they’re eating.

So it’s possible that eating 1600 calories a day  of a Mediterranean diet may result in greater   weight and fat loss than eating 1600 calories  a day in just a general calorie reduction. A calorie-unrestricted Mediterranean  diet doesn’t seem to do much for obesity,   so researchers are thinking  that reducing calories is still   more important than the specific  nutrients you get on the Med diet. And finally, there’s total mortality.

Cohort studies do indicate that  eating a Mediterranean diet is   associated with a reduction  in total overall mortality. The evidence here is merely “suggestive”  though, because it’s really hard to do   long-term intervention studies where the  outcome you're measuring is, you know. Death.

But, it makes sense, given that the  Mediterranean diet is associated with   a lower risk of death from all of the  specific causes we just listed out. But it’s not just that. The diet is also associated with longer telomeres.

Telomeres are sections at the  end of chromosomes that are known   to be shorter in connection with cell  damage through stress and inflammation. They are typically what people talk  about when they say “cellular aging”. Longer telomeres indicate slower  age-related biological processes,   which could result in lower mortality.

But researchers are still trying  to figure out exactly why the   Mediterranean diet has such broad health effects. One approach is to look at the different  parts of the diet as individual pieces. For example, the high intake of fruit and  veggies may be what impacts cognitive   functioning, and the inclusion of nuts  may be the reason for better heart health.

If that’s the case, then the reason that  the Mediterranean diet has so many health   effects would be that there are so  many different healthy parts of it. But there does seem to be  more to it just than that. Researchers are now studying the way  that the different parts of the diet   and different nutrients interact with each other.

One hypothesis is related to inflammation and  oxidative stress, which can cause cell damage. That cell damage can lead to  cardiovascular disease, cancer,   dementias, and diabetes, just to name a few. And there’s evidence that the Mediterranean diet   improves several different indicators  of inflammation and oxidative stress.

Now, we still don’t know the specific pathway by  which the Med diet might calm down inflammation. It may be that the nutrients involved tamp  down on things that cause inflammation,   ramp up things that prevent inflammation,  make cells more resistant to inflammation,   or change the way the immune system communicates. Whatever the mechanism, though,  it seems that the Mediterranean   diet has some really important  system-wide effects on our health.

Even better, the Mediterranean  diet isn’t just good for people. It’s good for the environment, too. Because it’s mainly plant-based,  it uses less water and has lower   greenhouse gas emissions than  many other dietary patterns.

And at least in traditional settings, the  meat that’s consumed comes from animals that   graze among tree crops that already  exist, as opposed to growing grains   specifically for animal feed, which  also lowers the environmental impact. But we are not doctors, and we can’t recommend you  switch to the Mediterranean diet for your health. What we can say, though, is that multiple  members of the SciShow team have had our   doctors recommend this diet to us,  so take that for what it’s worth.

But I for one have never turned  down an excuse to eat more hummus. And if that happens to make me  healthier, that sounds like a win-win. [♪ OUTRO]