While diets like keto and carnivore can be great for weight loss, they also come with an increased risk of heart disease and other disease.

Studies performed in the 1950s found that rates of heart disease were lower in countries like Italy, Greece and Spain than most countries in the west, which initially piqued the interest of scientists in the US.

Pop star Selena Gomez says that the Mediterranean diet even 'saved her life' after she was diagnosed with the autoimmune disease lupus in 2012.

Doctors and nutritionists have sung the praises of it as well, with countless studies backing up claims that it can help fend off Alzheimer's, cancer, heart disease and expand a person's lifespan.

A Spanish research team described the diet as a 'gold standard' of preventative medicine in 2016 after a meta-analysis linked it to a higher quality of life and lower risk of chronic disease.

Researchers gathered data from 19 studies across 2015 and 2016 that found that people who eat these diets often have lower blood pressure, coronary artery disease, heart disease, and stroke rates.

In 2016, Italian researchers published a massive study that followed 1,712 people over 50 years to see how the diet would affect their lifespan. .

Harvard University researchers were a part of a 2018 study finding that people who subscribed to the diet had biomarker indicators showing they were less likely to develop heart disease in the future.

Among the 26,000 participants, Mediterranean diet eaters had lower levels of inflammation, insulin resistance, hypertension and fats in the blood. .

A wealth of studies has tied the diet to lower cancer risks, and it can even be beneficial to a person after being diagnosed with the devastating disease.

University of Texas researchers found last year men suffering from prostate cancer could stem the progression of the disease with a Mediterranean diet.

The NIH says that a lack of calcium in the diet can also lead to low bone density.

Low-carb diets have also been tied to increased heart disease mortality. .

A 2013 meta-analysis of 13 studies by Japanese researchers- including nearly 250,000 participants - found that people who ate the diets were 31 percent more likely to die of heart disease.

In the group of studies, people who used intermittent fasting were less likely to develop coronary artery disease or diabetes. .

A Brazilian study published in 2018 found that people who took part in intermittent fasting recorded higher levels of HDL - dubbed 'good cholesterol' - and lower levels of the 'bad' cholesterol LDL and triglycerides.

High levels of LDL and triglycerides can lead to the walls of a person's arteries hardening, restricting blood flow and increasing the risk of heart disease, a heart attack or stroke.

The research, which included survey data from 24,000 people over 40, found that eating only one meal a day instead of three significantly increases mortality and heart disease risk.

Little research has been done on the carnivore diet, which is still a fringe diet with relatively new origins.

A diet made up entirely of meat and eggs can lead to high blood pressure, and heart problems.

The paleo diet is a style of eating that ditches foods that were not available to our earliest ancestors.

The diet is similar to keto, as many carb-rich foods like bread and rice are abandoned. .

Vegetables like broccoli, carrots and potatoes - that a ketogenic person may avoid - can give a person on the paleo diet their fix of carbs, though.

A 2015 meta-analysis of four studies, with a combined 159 participants, found that people who switched to a paleo diet during a study period saw their waste measurements drop more than those on other diets.

Anne Hathaway (left) and Miley Cyrus (right) are both advocates of the paleo diet.

Researchers from the University of California, San Francisco, found in 2015 that type 2 diabetics who switched to a paleo diet had greater control of their blood sugar and blood that was more sensitive to insulin

In the most extreme examples, people will adopt forms of the carnivore diet where the even eat raw meat - swearing off cooking as a modern form of food preparation

Cutting out all processed foods from a person's diet can be extremely beneficial to a person's health, however

This type of diet can lead to some vitamin deficiencies

A Swedish research team published a 2007 study finding that despite overall improvements in health, people who switched to a paleo diet were only getting half as much calcium from their diets

Harvard University experts also warn that the paleo diet could leave a person deficient in B vitamins

The most popular alternative diet in the world is vegetarian. 

In turn, they are also less likely to suffer from heart disease, according to a University of Oxford study published in 2019 that took place over 18 years and included nearly 50,000 participants

Researchers found that vegetarians and pescatarians had 13 percent lower rates of heart disease than people who ate meat

Removing meat from a person's diet can lead to iron deficiencies. 

This can be especially harmful for older people, where calcium deficiencies lead to brittle bones and the development of bone-stripping arthritis.