Sir Paul McCartney, 70 and still rocking, says being a vegetarian accounts for a lot of the happiness in his life. Although you don’t have to abandon all poultry and fish to upgrade your attitude and roll back your brain’s RealAge (yes, red meat is out), you just might want to Listen to What the Man Said.

Recent studies show that eating a veggie-intense diet makes you happier. We say: Clearing the junk out of your meals — saturated and trans fats in meats and prepared foods; refined carbs (that’s any grain that’s not 100 percent whole); added sugars and sugar syrups (they’re everywhere) — gets body and mind feeling great.

Here’s how to raise your spirits and your smarts:

Step 1: Get more omega-3 DHA from algae-oil supplements and foods like walnuts, ground flaxseed, trout and salmon. It protects your eyes from macular degeneration, your heart from abnormal beats and your brain from dementia, and it improves memory and quells anxiety.

Step 2: Amp up your veggie intake, and your brain will say “thanks.” Eating two or more servings of veggies daily decreases decline in thinking by 35 percent over six years. (Seventy percent of Americans don’t eat even two servings a day.) Another tip: French fries don’t count as a veggie.

Step 3: Eat whole grains to stabilize blood sugar levels. They prevent mood swings and keep you focused and clear. Six walnut halves or two tablespoons of apple cider vinegar before a meal, or 3/8 teaspoon of cinnamon daily also are great for healthy glucose levels.

The You Docs — Mehmet Oz, host of “The Dr. Oz Show” and Mike Roizen of Cleveland Clinic — are authors of “YOU: Losing Weight.” To submit questions, go to www.RealAge.com. A King Features syndicate.