Gentlemen, if you want to keep your sperm swimming — and who doesn’t? — head on over to the nearest fish market and load up on tuna and salmon.

The fattier the fish, the better — because the same fatty acids that make these fish such healthy choices for everything from your heart to your eyes to your brain are also positively critical to your fertility.

The omega-3 fatty acid docosahexaenoic acid (DHA) is one of the essential building blocks of sperm — and a new study on mice shows how it’s also a key part of the acrosome, which is what enables the sperm to penetrate the egg.

You might say it’s the most important part of all. The mice would agree: When they were denied DHA, they produced fewer sperm — and the ones they did create were misshapen, rendering them infertile.

But once DHA was put back into their diets, they began to produce again like, well, mice. (Side note: There has to be a pest-control angle in here somewhere).

This is, of course, just one study on mice. But human studies have also shown how high levels of these essential fatty acids can boost your fertility.

One study from just a couple of years back found that fertile men tended to have higher blood levels of omega-3 fatty acids, while infertile men had higher levels of omega-6 fatty acids.

And these days, with diets heavy in grain fed animals from factory farms, most of us get less of the desirable omega-3s and far more of the undesirable omega-6 fatty acids.

Call it one more reason to switch to fresh all-natural grass-fed meats.

Naturally, omega-3 fatty acids aren’t the only answers for sperm health. A lot goes into male fertility — and studies over the years have shown that high levels of vitamin D can boost the speed and forward motion of sperm, an essential trait called motility.

Other studies have also shown that junk food, soda and the BPA used to line canned goods (including soda cans) can slash sperm levels and turn the ones that are left into the microscopic equivalent of couch potatoes: slow, lazy and uninterested in the quest for the egg.

That would explain the recent rise in male infertility.

“Fish is brain food” is the kind of age-old folk wisdom that’s been proven time and again by cutting-edge science — and the latest research confirms that the best way to keep your brain swimming in gray matter is with a steady diet of fish.

I mean that literally: Seniors who eat fish at least once a week have more of that critical gray matter, giving them a lower risk of dementia and Alzheimer’s disease.

The biggest boost is in the frontal and temporal lobes — specifically the areas most closely linked to memory and learning, or exactly where you want your extra gray matter to be.

And if you think the benefits inside the brain are impressive, you should see how that translates out in the real world: Just 3.2 percent of the fish-eaters developed cognitive decline over five years, versus 30.8 percent of those who ate little to no fish, according to data presented at a Radiological Society of North America meeting.

If there’s one area where the researchers found no benefit, it was in fried fish — and I have to wonder if it’s because of the frying… or because of the oils people tend to fry things in.

Most people don’t fry their foods — fish or otherwise — in healthy oils. They fry them in the unhealthiest polyunsaturated oils of all, including blended vegetable oils, soybean oil and safflower oil.

Try a healthier oil — like peanut oil — and all your fried foods will get a health boost (and taste better, too).

But let’s get back to seafood, cooked however you like — because a diet rich in fatty fish will do so much more than protect your brain. Fatty fish can help prevent heart disease, protect your vision, beat depression and even improve your gums.

Yet despite all those benefits, some simply won’t eat fish to save their lives. Maybe it’s the smell… the taste… the texture… or all three.

Whatever the reason, you don’t have to actually eat any fish at all to get the benefits — because almost all of those benefits come from the omega-3 fatty acids found in fish oil, which you can find almost anywhere as a supplement.

Shop around before you commit to one — some brands will leave you with the “fish burps,” which is a little counterproductive if you’re taking pills to avoid the taste of fish in the first place.

Buy smaller sizes or sample packs first — it might take a little trial-and-burping, but eventually, you’ll find one that works for you.

You don’t need to hunt wooly mammoths to be a “caveman” these days. In fact, you don’t even need a cave.

The “caveman” diet is more about what you eat than where you live — and if you can stick to a 100-percent natural lifestyle of fresh meats and vegetables with no processed foods, congratulations.

You’re officially a caveman.

It’s hard to find anything wrong with this diet, and science now confirms what should have been obvious all along: Eating only fresh foods can help put you in the best shape of your life and slash your risk of illness and disease.

Researchers at the University of California San Francisco asked a group of unhealthy people to stick to a “caveman” diet high in healthy fats and proteins from meats, fish, and nuts as well as generous amounts of fresh fruits and veggies.

After just two weeks, everyone’s blood pressure and cholesterol levels plunged — with triglycerides alone falling by an average of 30 points.

“That’s the kind of drop you get by taking statins for six months,” Dr. Linda Frasettom, who led the research, told Medical News Today.

I’d almost agree — except statins come with a risk of severe muscle pain, liver problems and kidney damage. A diet of fresh natural foods will do none of those things to you.

Statins can even increase your risk of diabetes — but a diet with no added sugars and zero processed foods will practically guarantee that you’ll never get the disease.

Dr. Robert Lustig, an endocrinologist at the university, says diabetics who’ve tried this back-to-basics approach have seen a reversal of the condition — and some have actually been cured.

That’s right. The “c” word — and while most of the media is of course only too happy to trash the diet and even mock the people who follow it, one reporter got an up-close and highly personal look at just how well it works.

Dr. Kim Mulvihill of the CBS station in San Francisco had been battling a weight problem and pre-diabetes when she volunteered for the UCSF study. In just 10 days, she saw dramatic changes to her cholesterol, blood pressure and blood sugar levels as well as a boost in energy.

She eventually lost 30 pounds, and after seven weeks was no longer considered a pre-diabetic — causing her own doctors to tell her to stick to the diet permanently.

If you’re facing your own battle with disease — or simply want to avoid ever having to worry about one — maybe it’s time to go caveman yourself.

Diet advice usually comes with a whole lot of don’ts: Don’t eat this, and don’t drink that.

So let me add one more “don’t” to the list: Don’t listen to all that mainstream nonsense… because you don’t have to give up your favorite foods to live long, and a new study proves it.

The only other “don’t” you really need is this one: Don’t eat sugar–because researchers have confirmed that it’s the quickest path to an early grave.

The researchers also say the best way to ensure a long and healthy life is through a diet high in what the mainstream considers healthy food: low-fat dairy, fish, vegetables and whole grains.

But don’t put down your steak knife just yet, because the researchers also found something else… something they weren’t quite as eager to discuss in the pages of the Journal of the American Dietetic Association.

Something they later admitted was “unexpected,” probably because it doesn’t jibe with all those “don’ts” you usually hear: People who ate the most meat and fried foods and had a steady, moderate drinking habit lived just as long as the so- called “healthy” eaters.

And that means maybe you don’t have to stick to poached chicken and salad greens after all.

In the study, researchers tracked more than 2,500 adults between the ages of 70 and 79 for 10 years, splitting them into six groups based on the types of food they ate most frequently: “healthy foods,” “high-fat dairy,” “meat, fried foods, and alcohol,” “breakfast cereal,” “refined grains” and “sweets and desserts.”

After adjusting for risk factors, they found that high-fat dairy eaters–think ice cream–had a 40 percent higher risk of dying during the study period, while the sweets-and-desserts crowd had a 37 percent higher risk of death.

That’s compared to the so-called healthy eaters… but that’s where the researchers lose some credibility here–because even though the seniors in the “meat, fried foods and alcohol” group were just as likely to remain alive as those on the supposedly healthy diet, they were practically ignored.

It was as if they couldn’t explain it… so they didn’t even bother to try, despite the fact that those eaters represented the single biggest group in the study, with nearly twice as many of them than in the supposedly healthy group.

Sounds to me like it’s time to fry yourself a steak, crack open a beer–and ignore all the “don’ts.”

Your diet is just one measure of how long you might live… keep reading for an even simpler one.