As I left the group of cyclists at the designated meeting spot in the grocery store parking lot, one of the guys I didn’t know very well asked if he could pedal along and pick my brain.

“I don’t need to lose weight,” he said, “but I’m wondering if eating better stuff instead of so much junk would help my cycling.”

“Without a doubt.”

“How can you know for sure?”

We rode at a relaxed, non-competitive pace. Only my thoughts raced.

What exactly was it, I wondered, that made me so resolute about this fact, so hellbent to consume only the healthiest foods? Did I really “know for sure,” for instance, that eating so-called high-performance protein and carbohydrates three hours before a long ride would provide more energy than eating a bagel smeared with jelly, butter, or cream cheese?

Yes, I did, I realized. In this situation, something superseded the scattering of studies that suggested otherwise.

“I know my body,” I said to him. “I know what it feels.”

(Kudos, congrats, and three attaboys to the perceptive readers who recognized that I answered his question with a variation of the theme to last week’s column: “You never know. That’s why you feel.”)

I then told him a story that I used in a column years ago about how I purchased freshly baked, soft pretzels as a positive-discipline reward for deserving students, decided to eat one (a close nutritional equivalent to the aforementioned bagel with jelly) in lieu of my typical three-hours-before-the-ride meal, and what happened as a result.

For the first two-thirds of the ride, the pedals were turning over effortlessly. The only ache was in my jowls — from smiling so much. It was one of those rides when all is right and I’m loving life.

And then I felt like a fool when I thought about all the time and money I had spent in the last 20 years creating a special concoction of so-called high-performance protein and carbohydrates to fuel my rides when a cheap convenience food that I loved was now doing the same. That feeling ended when I attacked a short, steep climb with everything I had.

Suddenly, it felt as if some cycling Satan had syphoned every ounce of energy out of my legs.

I did the rest of the ride in what I call survival mode. That experience — as well as a number of other, less-dramatic ones — is how I “know” what you eat affects the quality of your workouts.

You too can use personal experience to “know” how to make sense of the recent conflicting research about the amount of protein that you should consume.

A few months ago, the results of a study published in the Journal of Nutrition contradicted a belief that had seemingly gained acceptance: that consuming “extra” protein (more than the recommended amount) along with weightlifting aided older folks in maintaining muscle, something that’s essential to maintaining a high quality of life as you age.

The men in this study whose average age was 70 and used a protein supplement shake while lifting weights three times a week for three months, however, gained no more muscle than the men in the study who did the same lifting and drank a placebo containing the same number of calories. Yet more recent research published in the Journal of Nutrition, Health & Aging reasserted the prior belief that older Americans need more protein.

In it, researchers reviewed the results of the 2005-2014 National Health and Nutrition Examination Survey focusing on the information provided by the more than 11,000 adults at least 50 years old who participated. The researchers hoped to discover some pattern between protein intake, overall diet, and physical function — and they did.

Participants who, according to the daily recommended intakes, didn’t consume enough protein ate significantly less greens, beans, and plant-protein foods, like soy, as well as less dairy and seafood. Moreover, they had a poorer diet overall, one generally lacking in a number of antioxidants found to promote health and delay aging, including zinc, selenium, vitamin E, vitamin C, and vitamin D.

About four out of every nine surveyed were not consuming enough protein. One-third of that group missed the mark by more than half.

Additionally, those over 50 who didn’t eat enough protein were more likely to find daily tasks like stooping, crouching, kneeling, standing for extended periods of time, and even preparing meals more difficult.

So how much protein do you need to consume during a typical day to feel your best?

The answer is a bit more involved than following the current recommendation of 0.8 grams of protein for every kilogram (2.2 pounds) you weigh, involved enough to require its own article. Read that next week.