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So I'm an 18 year old woman, 5'5 (166cm) and 171lbs (78kg). I want to lose about 10lbs max, I've been working out for about a year so the weight isn't all fat, I also have some muscle. I work out 3-4 times a week. I've entered this information into multiple iifym calculators and the results were all pretty similar, so I'm gonna post the one from the official iifym website.

Total calories: 1716

Protein: 131g

Fat: 69g

Carbs: 144g

BMR: 1567

TDEE: 2145

These macros seem way too high? If I'm not mistaken, the more you work out, the more you should eat.

Just to give you and example, 3 days ago I burnt 618kcal which would bring my macros to somewhere around 2300, and I only ate 1850. Yesteday, I burnt 371kcal which brought my macros up to somewhere around 2000, but I ate 1714.

I also used the lifesum app which put my macros to 1655kcal a day. Is that the correct amount?

I guess I'm looking for advice on how much I should eat, on days when I work out and on days when I don't, because I'm assuming those calories should vary, but if they shouldn't, please correct me. I'm worried if I eat too much I'll gain weight but I'm not sure if eating too little would be good too.

  • May I ask how you are measuring the food you eat? I suspect that you are underestimating the total calories you are eating in a day. – JohnP Oct 17 '18 at 14:09
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Use this video to understand the formulas yourself and substitute in appropriate values. I think you're overestimating your lean body mass. Get a DEXA or use the formulas as shown in the vid I linked.

If you plan on having a hard workout, throw in some more carbs (after figuring out your correct macros) on that day. If not, cut down on the carbs for that day. This is pretty standard weight loss procedure. Also remember, formulas are generalizations. They're meant to be a place for you to start out. Every body is different. Figure out what works for you and stick with it, experimenting as you go along. If you start hitting plateaus in weight loss (not just water fluctuations but actual over a week or two averages), change up your macros or throw in more cardio. There are various techniques you can try like caffeine for appetite suppression, intermittent fasting, higher fiber in your diet to keep you full etc. but at the end of the day, you do what works for you and gives you results.

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                                                  Maintenance

An easy rule of thumb is a person's maintenance calories i.e. how much they eat to maintain their current bodyweight is,

  • weight in pounds * 15

For example, a 200 pound person would be eating 3,000 calories per day to maintain that 200 pounds.

It's not ironclad as some people are more active so they might eat more, or some are really sedentary so they might eat less, but it's a very good starting point. (I can't remember where this originally comes from, but it's one of those old folklores of exercise science that has merit.)

                                                  Losing Weight

From that, one's bodyweight * 10 is a good starting point for losing weight. As you've seen, your bodyweight, 171 lbs, multiplied by 10, gets you to ~1700 calories, which is what the calculators have told you.

Pretty much every client of mine I've gone over this with has your initial reaction, "That seems like a lot of calories."

That's not surprising though. The numbers jump all over the place, but on average people will underestimate how much they eat so much it's not scientifically valid to even ask people in a research study for their own assessment.

  • One study showing people may underreport anywhere from 300 to 800 kcal per day

                                   Simpler = Less likely to trick yourself

This is a long way of saying I wouldn't bother with trying to get that fancy with your eating. Like trying to change it day to day based on whether you workout.

Because the other issue then is properly estimating how many calories you burn from a workout.

This is where again people are way off the mark, but this time in their overestimation.

For instance, many calculators will ask how many minutes the person worked out and at what intensity.

People invariably misjudge how intense the workout was in absolute terms. To them it might feel hard, but the calculator's version of hard may mean bordering on a professional athlete's intensity.

Next, the person will put in e.g. one hour of lifting weights. Sure, they were at the gym for an hour, but they weren't actually lifting weights that entire time.

Finally, there are only so many calories you can burn in a day from activity. After about 400 calories, the body starts to compensate in other ways to minimize how many calories over the course of a day that will be burned.

There are all kinds of ways we trick ourselves with eating. Telling people a granola bar is low fat will actually end up causing people to eat more than if they aren't told that. People knowing or subconsciously say to themselves "It's low fat, so I don't have to worry as much about how much of it I eat." (The Dieter's Paradox.)

                                                  Practicality

Lastly, focusing on how many carbs, protein, fat, calories, manipulating it day to day, that is for many asking a lot.

When you factor in a job or school, social events, being that particular gets very hard.

It's just much, much easier to eat a given amount each day. It's better to not even open the door to "Well, I exercised a lot today, so I can eat..."

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