• They help "the human body to activate stem cells, undergo cellular reprogramming and then regenerate parts of organs and systems."
• but if you're committed to changing your diet long term, then following the FMD as often as possible while maintaining a normal muscle mass, or trying the longevity diet, is a much better choice, he says.
• A longevity diet should be low in protein, but include a sufficient amount of protein, Longo says. [This is confusing? What does he mean? low but sufficient? How?] He also suggests avoiding red and white meat [what is white meat? Give an example. Chicken? so does he say no meat at all?] meat and having two, three eggs a week. Generally he says you should eat "very little cheese [and] very little animal-based products."
• A longevity diet should have protein, but no more recommended daily serving, and consist of "very little cheese," Long says. He also suggests avoiding red and white meat and to generally go light on animal-based products.

For a long and healthy life, what you eat, and how, is what's most important, says Valter Longo. "Some dietary interventions are much more powerful than we had imagined," he tells CNBC Make It.

Longo has studied longevity for about 20 years in Italy, but began researching the topic in 1989. Using animal models, like mice, he and his fellow researchers found that certain diets can repair cells, reduce inflammation and increase the efficiency of cancer treatments like chemotherapy.

"The human data is starting to indicate this is probably true also [in] humans," he says. "But there are more clinical trials needed to know what the mechanisms are in people."

Still, he says it is possible to eat in a way that promotes good health and longevity — and even help reduce your risk of developing cancer.

Following these two diets can contribute to good health and a long life, expert says

1. Fasting-mimicking diet

Longo is the director of the Longevity Institute of the Leonard Davis School of Gerontology at the University of Southern California-Los Angeles, and developed the fasting-mimicking diet. The FMD is a 5-day diet "high in unsaturated fats and low in overall calories, protein and carbohydrates."

Adhering to the diet involves fasting for 12 hours a day, for the five days: "You eat, say 8 a.m. to 8 p.m., and you fast 8 p.m. to 8 a.m." Longo says.

Longo suggests cancer patients fast for about 14 hours a day, in five-day intervals. A 2017 study published in JAMA Oncology found that women with breast cancer who fasted for 13 hours or more had a lower risk of breast cancer recurrence than women who didn't.

"The 14 hours should not be combined with the actual cancer treatment," Longo advises. "Let's say they get chemotherapy once a month, then they should stop a few days before."

Wait a few days after treatment before starting the diet again, he adds.

Practicing the FMD just two to four times a year can greatly benefit people who follow the standard American diet.

2. Longevity diet

Longo's "longevity diet" draws from a lot of different things, most notably the Okinawa and Mediterranean diets.

He says adhering to the diet means your daily meals include the following:

• Mainly vegan ingredients
• Generally low in fruit, but high in vegetables
• Tree nuts
• Whole grains like brown rice and quinoa
• Legumes
• Fish (3-4 times a week)

A longevity diet should have protein, but no more than the recommended daily serving, and consist of "very little cheese," Longo says. He also suggests avoiding red meat and white meat, like chicken and turkey, and to generally go light on animal-based products.

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