More than 30 years ago, I first kept a comprehensive food journal in order to reach an unnaturally low body weight in the hopes of running a sub-2:40 marathon. (I missed the mark by 49 seconds, sorry to say, despite achieving my goal weight.)

A degenerative knee condition stopped me from running soon after that, but I haven’t stopped recording my food intake. Doing so not only allows me to keep my weight where I want it, but also to learn how what and when I eat affects my mood, energy level, and physical performance.

One additional unexpected perk: I’ve developed an uncanny sense of how many calories my body needs.

Years ago, for instance, I baked 1000 grams of potatoes, scooped out and mashed the insides, added 4 ounces of fat-free cup cheese, and placed the mix back into the skins. I then transported my supper to my parents’ house where my mom insisted on serving me.

While I use a toaster oven to reheat my version of twice-made potatoes, mom used a microwave. The change made the skins rubbery instead of crisp, but that wasn’t the biggest difference I noticed.

It was my level of hunger ninety minutes or so after the meal.

I had prepared that same meal many times before, weighed out to the same amounts, and it had always been satisfyingly filling. What was different this time?

I shared my theory with my parents. “The microwaving” I told them. “The microwaving must break down the starch in the potatoes quicker.”

The next morning, my mother called to tell me my theory was probably wrong and the reason why. It came in the form of an apology.

“Two of the skins must have fallen off the plate while in the microwave. Sorry,” she said. “I only noticed them in there this morning.”

But I was far from upset that mom had shortchanged my supper. I was psyched. This was proof, in my mind, that I had become so attuned to my body that I could detect a 150-calorie deficit over the course of a 3000-plus calorie day.

A recent study conducted at Sheffield Hallam University in the United Kingdom, and led by Dr. Steven Brown, however, suggests that my acute sense of calorie consumption is rare rather than run-of-the-mill.

The researchers came to this conclusion by lying to their 26 study subjects. On one day, the 26 were told they were being served a two-egg omelette. On other day, they were told the omelette they ate contained four eggs.

On both days, though, each omelette contained three eggs.

After each meal, the 26 were questioned. When the subjects thought they had consumed two eggs, most recorded greater feelings of hunger and lower feelings of satiety when questioned two hours later.

Furthermore, all 26 not only ate more at lunch but also more during the rest of the day.

The opposite proved true to some degree, too. When the subjects thought they had consumed four eggs, they ate less throughout the day.

The researchers could find no physical cause for the difference. Blood samples after each meal showed no significant deviations, and the levels of the hunger hormone ghrelin after both meals were remarkably similar.

At the annual conference of the British Psychological Society’s Division of Health Psychology, Dr. Brown and his team hypothesized why this occurred. They dubbed the phenomenon “expected satiety” — how full you expect to feel after a meal — and noted that expectation plays a major role in how full you actually feel as well as how much you will eat after that.

In other words, Brown and his colleagues are telling you not to trust your gut when it comes to how much you put — or think you put — into it. Their study shows they have a point, especially when you consider it reinforces their findings from a previous study.

Prior to this, the researchers found that subjects could be fooled into eating more or less by being fooled about the composition of a smoothie they drank.

These two studies and the personal story I shared support something that I’ve written more than a few times: There’s no fooling yourself if you keep a food journal.

While you may argue that weighing foods and writing down the caloric totals is a big hassle, I’d argue that the so-called hassle is really something that so many are seeking: information important to you.

Isn’t that desire what has spawned the sickening success of social media? In fact, there are now even apps that do the job of food journaling for you.

I can’t attest to how effective they are, though. I’m old school. I like entering my info into a 5”x8” notebook.

I find the act of writing forces reflection and leads to greater retention, which heightens my awareness.

But if using an app helps you achieve all this — and maybe even accurate caloric assessments! — don’t hesitate to use one.