The sun was beginning to set on the day after Hayashi had decided to go on a diet.
"Yamamoto, want to go get dinner?"
She was asking me to head to the supermarket.
Come to think of it, I’d completely forgotten about our exchange from the day before, but I was supposed to be helping her with her weight loss.
"Sure."
We left the apartment together. Our destination wasn't the store nearby, but one about a kilometer away.
"We have to walk, after all," Hayashi suggested.
Looking at her, I noticed she was already sporting a brand-new set of running wear. She was clearly motivated.
"Just exercising aimlessly isn't going to do you any favors," I said, immediately dampening her spirits.
"Huh? What's wrong with walking?"
"First off... do you actually understand the mechanics of how people gain weight?"
"The mechanics of getting fat?"
Hayashi gave me a suspicious look. She thought about it for a moment, then narrowed her eyes at me.
"Isn't it just a lack of exercise or eating too much?"
"Why are you glaring while you say that?"
Good grief. This girl was combative about everything.
"Let me ask you this, then: how much exercise qualifies as 'enough,' and how much food constitutes 'eating too much'?"
"I don't know."
"Hmph."
"Don't give me that triumphant look."
"Listen. The principle behind weight gain is actually quite simple. In short, if your calorie intake exceeds your expenditure, you gain weight. Conversely, if your expenditure is higher than your intake, it is physically impossible for your weight to increase."
That was the conclusion I’d reached back in high school when I was researching fitness alongside my weight training. I’d seen plenty of trainers online explain it the same way, so I was fairly certain I was right.
"In other words, people don't get fat specifically because of a lack of exercise. They get fat because a lack of exercise reduces their calorie expenditure. Likewise, they don't get fat simply because of overeating; they get fat because overeating increases their calorie intake."
"...And?"
"I can read you like a book. You were planning to drastically increase your exercise while starving yourself, weren't you? And you were going to be extreme about it."
"Ugh..."
Bullseye.
"My point is that you don't need to do anything that drastic as long as you calculate your calories properly. It’s like I told you during the bookkeeping exam: vague plans don't last. You’ll just end up overextending yourself."
"...Fine. So what should I specifically do?"
"First, we make a plan."
Our conversation continued as we walked past the closer supermarket.
"I mentioned intake and expenditure earlier. To be precise, to lose one kilogram of body fat, you need to create a deficit of roughly 7,500 calories."
"How do you even know such specific numbers?"
"Because I looked it all up in high school." I cleared my throat. "Anyway, if it takes 7,500 calories to lose one kilo... then we just need a goal. First, how much weight do you want to lose, and by when?"
"...Christmas is in two months. I want to be thinner by then."
"You ga—... I mean, I don't think you need to lose as much as you gained."
I was about to mention her actual weight gain out loud, but she gave me a look that could kill, so I just used my fingers to indicate the amount.
"Maybe just half that? Being too thin can cause health problems, too."
"...Yeah."
"So, if we're looking at five kilos in two months... you basically need to lose one kilogram every two weeks."
"Okay."
"That's 7,500 calories every two weeks. Or, roughly a 500-calorie deficit per day."
"Is that it?"
"To put it in perspective, a 500ml juice is about 200 to 300 calories. One onigiri is about 200."
"Wait, is that all it takes?"
"Well, if we get technical, we'd have to talk about basal metabolic rate and the fact that you don't drink juice every day, but my point stands: a 500-calorie daily reduction isn't that hard to achieve."
"...I guess not."
A happy smile spread across Hayashi’s face.
"Yamamoto-sensei! I'm actually starting to feel motivated now."
"Who are you calling 'sensei'?"
It was more than a little disconcerting to have the girl formerly known as The Queen call me that.
"A-Anyway... the point is you don't need some reckless, vague diet." I shook off the embarrassment and continued. "Starting today, use a calorie counting app to track your intake."
"Can't I just keep a rough estimate?"
"No. An app will track your three main nutrients, too. If you focus only on cutting calories and neglect your nutrition, that's bad."
"I see... Like, I'll get irritable?"
"Haha. Your irritability has nothing to do with your nutrition, does it?"
She punched me in the shoulder.
Hard.
"...My apologies," I managed.
"Hmph."
"...Also, starting today, you're using my body composition scale. That way, we'll get a rough idea of your current metabolism, which makes calculating your expenditure easier."
"Fine."
Good. Step one—the visualization of Hayashi's intake and expenditure—was complete.
Now for the next part.
"Next, we talk about exercise."