[Author’s note: This is the second part in an occasional series about weight loss and fitness. Click here for the first part.]

Who wants to lose weight, feel great, and live a long and healthy life? As expected, everyone has raised their hand.

OK, put your hands down now. What does it take to achieve these goals? Diet and exercise are equally important in long-term health, but let’s look at what recent science is telling us about the healthiest diets.

Part one of this occasional series suggested a three-part recipe for losing weight and feeling great: 1) honestly assess your level of will power so that you can phase in your diet and exercise changes accordingly; 2) create a diet and exercise plan based on your self-assessment, research and the lifestyle changes you think you can achieve in a sustainable manner; 3) experiment with different approaches and eventually settle into what you find works for permanent lifestyle changes.

I intentionally didn’t go into much detail in my last piece about what exactly you should eat. This is because we all have different tastes, habits and — again — different levels of will power for changing our ingrained habits. And, frankly, there’s a ton of contradictory advice and evidence about which diets are best, so I didn’t have space to delve into this in any detail.

This piece, however, will look at what the best science is telling us about a healthy diet. I’m going to rely heavily on University of Southern California professor Valter Longo’s work because I consider it to be the gold standard for nutrition research, and his recommendations in his book The Longevity Diet are well-supported with both data and good logic. Longo is the director of the Longevity Institute at USC and the IFOM Program on Longevity and Cancer in Milan.

He comes from an area of Italy known for very long lives, and part of his research focus has been looking at similar areas around the world and why those people live so much longer than normal.

Longo’s Longevity Diet

The short summary of Longo’s “Longevity Diet” is as follows:

» Eat mostly plant-based (vegan) with occasional low-mercury fish or other seafood (two or three times a week), and lots of nuts and olive oil.

» Generally eat modest amounts of protein, whether it’s plant-based or animal-based.

» Very limited or no dairy; goat’s milk and cheese are OK.

» Minimize saturated fats and sugar.

» Eat foods from your ancestral homelands as long as they are otherwise healthy.

» Eat two or three meals a day, ideally two solid meals and one snack, in a 10- to 12-hour window, and don’t eat three to four hours before bedtime.

» Take multivitamins every three days.

» A few times a year, if you are under age 65 to 70 and otherwise healthy, do a five-day water fast or a “fasting-mimicking diet,” which includes food but mimics the benefits of actual fasting.

Longo’s Longevity Diet is what I call a “plant-centric” diet, which means the large majority of what you eat is plants, fruits, nuts and legumes. It’s not going to kill you to eat occasional meat or dairy, but for those younger than age 65, Longo recommends you keep these very low or absent in your diet. For those older than 65, Longo recommends eating higher portions of animal protein along with good sources of plant protein because our bodies are programmed to lose muscle mass as we age.

Longo argues against a strictly vegan diet or cutting out oil, as some researchers have recommended. He argues that consumption of fish, nuts and olive oil is associated with reduced risk of heart disease as well as very long lives in communities in Japan, Greece and Italy (the famous “blue zones” where people are living to 100 years old far more than the average population).

There are definitely good ethical and environmental reasons to be a strict vegan, and a later piece will examine these arguments, but Longo argues that being strictly vegan — as opposed to mostly vegan — is not optimal for human health.

Longo advises strongly against the various “keto” diets that include high animal protein, high fat and low carbs. While these diets will help you lose weight in the short term, through increased ketogenesis, they are likely to lead to potentially serious health problems down the road.

Longo writes: “If we examine the laboratory studies, we see that both high protein intake and high saturated fat intake are associated with aging and disease, an additional and key vote against a high-protein, high-saturated-fat diet.” If there is any doubt, he adds later in the book that this kind of diet is “the worst of all possible regimens” for overall mortality risk, cancer risk, heart disease and diabetes.

In short, diet and good exercise may be the magic pill for health and longevity that isn’t available (yet) in actual pill form. Longo doesn’t promise immortality, of course, in following his recommendations. But he does suggest we’ll maximize our chances of living to a hundred or more.

The new science of fasting

I’ve followed the development of nutritional science from the sidelines for some time now. Beyond the various fad diets that have come and gone, it seemed to me that author Michael Pollan got it pretty much right in his well-known book The Omnivore’s Dilemma, in terms of basic eating advice: “Eat food, not too much, mostly plants.”

Unpacking Pollan’s statement a little, his point of view is that we should eat real, whole foods, not overly processed, pretend foods; we should stick mostly to plants, fruits and nuts, with occasional meat and fish to taste; and we should eat moderately.

This is still great advice. My mom swears by it, and rightly so.

We are now at a point, however, because of the efforts of researchers like Longo and many others, that we can make more specific recommendations based on well-established science.

Longo probably would agree entirely with Pollan’s little three-part mantra, though he doesn’t discuss it explicitly in his book. Where Longo goes beyond the mantra is in his recommendations on intermittent fasting and the fasting-mimicking diet.

As mentioned above, Longo recommends eating within a 10- to 12-hour window each day, which is a type of intermittent fasting. He also recommends two or more times a year engaging in either a water (no food) fast or a fasting-mimicking diet that achieves the same or similar results as actual fasting.

The benefits of caloric restriction and intermittent fasting are now well-established. We don’t really understand yet why evolution built us this way, but it seems that when we stress our body by mimicking mild starvation, it responds by cleaning things up inside our cells, as well as killing off sickly cells and, more generally — as Josh Mitteldorf argues here — by slowing down many of the programmed aging aspects that are built into our genes. This includes increased telomere length, which is another topic I’ll cover in a later article.

Longo stresses many times in his book the need to consult with a doctor or other medical professional before engaging on any fast longer than a day.

Can diet really prevent or even cure disease?

This brings me to what is perhaps the most groundbreaking area of Longo’s research — the fact that he and other researchers now have developed a body of work that shows remarkable preventive and even curative effects of diet, fasting and exercise on many serious diseases: “[G]enetic or dietary interventions can not only delay diseases but actually eliminate a major portion of chronic diseases in mice, monkeys and even humans to extend longevity.” Mice fed various versions of Longo’s longevity diet have lived up to 40 percent longer than average.

Longo presents good data showing that the diet he recommends not only will lead to optimal weight and health but also provide strong protection against the major ailments of old age, including cancer, cardiovascular disease and diabetes, and even Alzheimer’s and other neurodegenerative diseases.

For example, Longo shows (citing a 2007 study by Willcox, et al) that cardiovascular disease and cancer occur with remarkably lower frequency among Okinawans, and the Japanese more generally, than among Americans. Longo and the study’s authors pin the difference on diet.

I’m embarking now on my own adventure using Longo’s longevity diet to improve my health and longevity. I’ll report back with some results at a later date.

A key benefit of Longo’s diet recommendations is that they can be eased in, and nothing needs to be eliminated entirely from your diet. For those who prefer not to go “cold turkey” on giving up things they like to eat, this can be a real benefit. Longo includes a two-week meal plan for getting started on the Longevity Diet, at the end of his book.

Contrary to what many might think, eating plant-centric (mostly vegan) can be very fulfilling and lead to all sorts of tasty new meals. I’ve been experimenting with veganism during the past couple of years, helped by my longtime vegan partner, and I’ve found that once you get past the notion that a “good meal” needs to have some kind of meat, a whole new world of tastes and satisfaction awaits.

— Tam Hunt is a lawyer and writer, and creator of the new Forever Young? blog on all things related to anti-aging.

Tam Hunt is a lawyer and a writer. The opinions expressed are his own.