Hey everyone, it's Mikki here, you're listening to Mini-Mikkipedia, and today I'm going to tackle one of those questions I get a lot with regards to why scale weight always tracks heavier than actual fat gain.

And I get comments and questions a lot from clients checking in with me and just people on social media saying, you know, my weight has skyrocketed by two kilos this weekend, or, you know, I've gained four kilos in three weeks, amounts that are sort of seemingly impossible.

And even if, you know, you have a big weekend, got Friday night dinner with friends and a couple of wines, then you've got brunch or long lunch on a Saturday, Sunday,

there might be some sort of family birthday. And then Monday morning, you step on the scales and you're up two kilos. And it's really easy to think, gosh, I've undone a month of work in this instance.

And of course, what you decide to do on Monday morning really depends entirely on what you think that that number means. So if you think it's two kilos of actual fat, then the logical response is panic.

You'll skip breakfast, you'll cut carbs, you'll punish yourself in the gym, you'll white knuckle your way through.

And that'll last two to three days before you crash and burn on Wednesday. But if you knew what that number actually was, I think that the response is a lot calmer and it's a lot more useful.

And I will say that you have to let your rational brain overtake the irrational and emotional thoughts that come with that increase in scale weight.

So if you've spent any time around nutrition, I'm sure you have heard that a kilo of fat is worth about 7,700 calories.

Or 3,500 calories per pound. That's actually a more recognisable number.

So the maths goes like this then. You eat 500 calories a day, more than you need, and in about 15 days, you've gained a kilo of fat.

Eat 100 calories extra a day, a biscuit or a decent splash of milk and a couple of coffees, and it takes about 11 weeks to gain that same kilo of fat.

Eat 1,000 calories a day and you're there in about eight days.

It's neat. It's tidy. It's been printed in textbooks, government websites, in apps, and of course, Instagram for decades.

Not Instagram for decades, but everywhere else. And also plenty of health professionals use it as well because it's sort of easy.

And it's, you know, it is a bit of a rough guide, if you like. The question is, really, does that even hold up?

And I'd say that the short answer is, well, sort of. And of course.

The long answer is what I'm talking about today. So let's dive in.

The figure traces back to a paper by Wyschnowski. He was a physician who published a short paper in 1958 in the American Journal of Clinical Nutrition called Caloric Equivalence of Gained or Lost Weight.

He pulled together what was known at the time and landed on that 3,500 calories for a pound of body weight gained or lost.

And if you convert that to metric, you'll get that roughly 7,700 calories.

And the logic is pretty reasonable. Pure fat contains around 9 to 9.4 calories per gram.

But the fat on your body isn't pure fat. Adipose tissue, the actual tissue, is mostly lipid, mostly fat, but it also contains water, protein, and the structural bits of the cells themselves.

So in a follow-up letter a couple of years later, Wyschnowski put the energy in adipose tissue at around 8.3 calories per gram.

So a little over 8,000 calories in a kilo of fat tissue.

So, I mean, that's not 7,700, obviously.

And that's because 7,700 was never meant to describe a kilo of fat tissue specifically.

It was his estimate for a kilo of body weight change on the assumption that most of the change would be fat tissue with a bit of extra stuff mixed in.

And super interesting, in the same letter, Wyschnowski pointed out that

So a gram of weight gained as glycogen or protein with its water only represents about one calorie of stored energy, compared with about eight for fat tissue.

So carbohydrate and protein, they are about four calories a gram.

But when they're stored with around three grams of water each, every gram of weight you gain as glycogen or lean tissue is mostly water and only carries about one calorie of stored energy.

So as an estimate of how much energy is sitting in a kilo of body fat, that number, 7,700 calories, is defensible.

But it isn't perfect because the composition of adipose tissue varies from person to person.

The problem is not necessarily that number, but it's what we've done with that number since.

We took that number about stored energy and turned it into a prediction about what happens when you eat more or less than usual.

And they aren't the same thing.

So, the first problem is that the extra food isn't the same as extra stored energy.

When you eat 500 calories more than usual, your body doesn't just open the door and file it all away.

Digesting, absorbing, processing food, all of that costs energy.

So when you eat more, you burn a bit more doing it.

Storing that energy also has a cost, and the cost depends on what you're storing.

When researchers put people in a whole room calorometer, which is essentially a sealed room,

that measures every breath you take in and out, so you can work out exactly what you're burning,

and overfed them by 50% above their needs for two weeks, the type of surplus did matter.

When the extra came from carbohydrate, the body ramped up how much carbohydrate it burned.

Total energy expenditure crept up, and around 75-85% of that extra energy was stored.

When the extra gap came from fat, fat burning barely shifted,

and 90-95% of fat was stored.

The gap was biggest in the early days of overfeeding.

So it doesn't mean that you gain more fat with carbs.

Three quarters or more of the carbohydrate surplus still got stored.

It just means that the body handles different surpluses differently,

and that straight line calculation assumes that it doesn't.

And protein? Well, protein is the most forgiving when you eat extra calories from protein.

And there are studies in trained lifters,

for example from Professor Antonio's group,

where people ate well over 4 grams per kilo and didn't really gain fat.

And these studies did rely on food diaries,

and when researchers ran the experiment properly with people living in a metabolic ward,

and every mouthful was measured, it did look a little different.

Overfed by about 950 calories a day for 8 weeks,

people gained the same amount of fat whether the diet was low, normal, or high in protein.

What protein changed?

What protein changed was pretty much everything else.

The higher protein groups gained around 3 kilos of lean tissue and burned more energy at rest.

So protein doesn't make your surplus disappear,

but it just changes what that surplus turns into.

And then of course there's movement, right?

And this is where it does get really interesting.

In 1999, Levine and colleagues at the Mayo Clinic,

they published a study in Science where they overfed 16 non-obese adults by 1000 calories a day for 8 weeks.

Same surplus for everyone.

And the amount of fat people stored varied tenfold between the lowest and the highest gainers.

And the biggest part of that difference comes down to NEAT,

or non-exercise activity thermogenesis.

That's the fidgeting, the standing, the pacing while you're on the phone,

the general moving around that isn't formal exercise.

And about two thirds of the increase in people's daily energy expenditure came from NEAT.

Some people ramped it up big time in response to all of that food.

And some people barely changed at all.

And how much somebody's NEAT went up predicted how well they resisted fat gain.

So two people eating exactly the same extra food can end up storing very different amounts of it.

And there was some, there was a twin study actually out of Quebec.

And it was led by Bouchard and colleagues and published in New England Journal of Medicine in 1990.

And they took 12 pairs of identical twins, all young men,

overfed them by 1,000 calories a day, six days of the week, for 84 days,

spread across a 100-day period.

This was supervised, so they knew exactly what went in.

Over the whole study, each man ate about 84,000 extra calories.

So if you ran that through that 7,700 rule,

then 84,000 divided by 7,700 is nearly 11 kilos.

And if the rule were a reliable prediction,

every one of those men should have gained somewhere around 11 kilos,

and most of that should have been fat.

But that's not what happened.

So the average weight gain was 8.1 kilos,

and of that, roughly 5.5 kilos was fat.

And the range was huge.

Same extra food, same supervision,

the lowest gainer put on 4.3 kilos,

and the highest put on 13.3.

That's a three-fold difference.

And interestingly, the twins tended to respond just like that.

There were about three times more variation between the pairs than within them.

And where they stored the fat,

how much went on the belly versus elsewhere,

how much ended up as visceral fat deep in the abdomen,

was even more similar within pairs.

So the author's conclusion was that genetics played a big role

in how you respond to a surplus.

How much of it you store, whether you store it as fat or lean tissue,

and where it goes.

And I guess one caveat which is definitely worth highlighting

is that these were young men.

We can't map those numbers directly onto a woman in her late 40s

going through perimenopause.

And nobody's really run this kind of tightly controlled,

long overfeeding study in that group.

Wouldn't that be interesting?

But the principle holds that the same surplus

does not produce the same outcome in different bodies.

And the second problem is that not all weight gain is fat.

So when you gain weight, some of it is fat,

some of it might be lean tissue,

but a lot of it, especially in the short term,

is glycogen and water.

Particularly if we're thinking about these, you know,

weekend benders, right?

Glycogen is how you store carbohydrate in your muscles and your liver.

And it's stored along with water.

So, as I said before, for every one gram of carbohydrate you store,

there's typically three to four grams of water that goes along with it.

So when you do top up your glycogen after a few days of eating more carbs,

the scales can jump quickly.

But it's not fat.

It's fuel and fluid.

There's a classic study from 1900,

1970,

by Olson and Sultan.

Researchers had people do a hard bout of exercise to drain their glycogen,

then eat a low-carb diet for three days,

then switch out to a high-carbohydrate diet for four.

Over those four days of eating more carbs,

body weight went up 2.4 kilos.

In total body, water went up 2.2 litres.

Almost all of that weight change from water

came along with the glycogen they were storing.

So, for athletes listening,

this is why you can be up a kilo or two

after carbo loading before a race.

But of course it's got nothing to do with body fat.

I will also just caveat here that

not everyone actually gains weight with a carb load.

In fact, a study came out last year showing exactly that too.

So, again, the way the body stores fuel is highly variable.

And there was another recent study

comparing moderate and high-carb intakes over a few days,

finding a difference of about 0.7 of a kilo in body mass,

tracking the difference in muscle glycogen.

What I will say is,

even though I always say three to four grams of water

come along with a gram of carbohydrate,

that exact ratio actually isn't that fixed.

So muscle biopsy work has backed up the idea,

but there are other studies that haven't found

such a tidy relationship.

So that's worth mentioning in case in your head you're like,

hang on, not all research shows that.

But it's basically, it's ballpark,

and it's the direction that really matters.

And then if I'm thinking back to a big weekend

of sort of eating and celebrating,

if you're eating out, there's extra sodium

that tends to come with that.

And that'll make your body hold more water.

Alcohol, that'll shift fluid around.

And in the physical weight of the food and drink,

that's still making its way through your gut.

If you're eating more food in total,

that's also going to register on the scale.

But again, it's not actually body fat.

And the third problem is energy balance is not static.

So that 7,700 rule,

as it's often used,

treats your body like a fixed calculator.

Eat X extra, you will gain Y amount of fat.

Forever, linear, in a straight line.

But as your body mass changes,

so does the energy cost it takes

to run and move that body.

Kevin Hall at USNIH

has done a lot of the work around here.

And in 2013, he and his colleague Chao

wrote a short piece in the International Journal of Obesity,

literally titled,

Why is that 3,500 kilocal per pound weight loss rule wrong?

And their answer is probably as nuanced

which you probably would expect

coming from the likes of Kevin Hall.

So they argued that most of the series error

isn't really that number, 3,500.

It's the assumption that the gap between what you eat

and what you burn stays the same over time.

And it doesn't.

Your body changes,

and you're expended to changes with it.

The body moves the goalposts.

They actually worried that people would walk away

thinking the problem was just the number,

and that swapping in a better number would fix it.

But because it is dynamic,

that's not going to work.

So I suppose that's where I say

that it's sort of correct,

but it sort of isn't.

Like this whole premise around that 3,500 calories

or 7,700 calories per kilo.

In another study published

in the New England Journal of Medicine in 1995,

where people were held at 10% above their usual body weight,

their total daily energy expenditure went up,

beyond what you'd expect just from being bigger.

Most of that increase came from that NEAT again,

non-exercise activity thermogenesis,

which is how much they moved.

So your body can push back against gaining weight

as much as it can against losing weight.

So ultimately,

the bigger problem isn't the number,

but it's how we apply the rule.

Having said that though,

there are researchers who have questioned the figure as well.

And when you look at what's happening,

and what they've found,

it does come back to Wyschnowski's original assumption

that most of the weight that changes is fat.

Because when you actually measure the energy content

of weight change in real people,

it isn't fixed at 7,700.

Hall has shown with modeling

that that figure I just mentioned

roughly fits people with obesity

who carry a lot of body fat,

more than around 30 kilos of it.

For leaner people,

it overestimates how big a deficit you need

per kilo lost,

because more of what they lose is lean tissue,

which holds far less energy than fat.

In early weight loss,

the energy per kilo lost can be much lower.

When Hamesfield's group tracked people

with body composition scans during the first months

of a calorie restriction trial,

the energy content of each kilo lost at week four

was just under 4,900 calories.

By week six,

it had risen to around 6,000,

and then it settled there.

That early phase is when a lot of what comes off

is glycogen and water rather than fat.

So they also found a sex difference

with each kilo lost by women

carrying more energy than each kilo lost by men,

around 6,800 versus 6,100 calories.

So what is the actual answer?

Well, I mean, everyone's got an opinion, obviously.

Here's how I'd frame it,

just after the digging that I did.

So when people say a kilo of fat,

they're usually blurring three different things.

That's a kilo of pure stored fat,

a kilo of pure stored lipid,

which is around 9,400 to 9,500 calories,

a kilo of adipose tissue,

the actual fat tissue on your body,

which is a little over 8,000 calories,

depending on how much of the adipose is actually lipid,

and a kilo on the scales,

which could be fat, water, glycogen,

gut contents, muscle,

or most likely a mix of all of them.

That kilo could represent anything

from about 1,000 calories,

if it's mostly glycogen and water,

to more than 9,000 calories if it's mostly fat.

7,700 calories tells you roughly how much energy

is sitting in a kilo of body weight that's mostly fat.

It doesn't tell you exactly how many extra calories

you need to gain a kilo of fat.

It's just not the same question.

So if a kilo of fat tissue holds a bit over 8,000 calories

and your body stores somewhere between three quarters

and almost all of a surplus,

depending on what it's made up of,

you actually need to eat somewhere in the region

of 9,000 to 11,000 calories

to add a kilo of actual fat tissue.

At 500 extra calories a day,

that's about three weeks,

rather than that 15 days original estimate,

and 1,000 extra calories a day,

that's around 10 days.

And that's before your body starts moving more,

burning more as it gets bigger,

and responding in its own particular way,

which, as the twins showed us,

can vary a lot from one person to the next.

So treat those numbers as a rough guide, clearly,

and not as like this definitive rule.

So if you go back to that big weekend,

and let's say you did eat 1,500 calories

over your needs on Friday, Saturday, and Sunday,

which is genuinely a big weekend,

that's 4,500 extra calories

spent by those extra drinks and a night out on Friday,

that birthday on the Sunday and the brunch on Saturday.

Even if every single one of those calories

was stored as fat tissue, which it won't be,

you're looking at a bit over half a kilo.

Once you account for the energy the body spends

handling and storing that surplus,

you're realistically looking at around 400 to 500 grams

at the very most.

And a fair chunk of that carbohydrate from the weekend

will have gone into topping up your glycogen first.

So of course, you can gain fat over a weekend.

But the two kilos on the scales on a Monday

is mostly glycogen,

water, salt, and food in transit.

When you go back to your normal way of eating,

a good chunk of it will be gone within a few days.

And then of course, that same logic applies in reverse, right?

So the first week of a new plan

where the scale drops two kilos,

a lot of that is glycogen and water as well.

And it's why the first week always looks amazing,

and the third week can feel like nothing is happening,

even when you're doing everything the same way

and you're actually seeing progress.

The fat loss is there all of the time,

it just wasn't the whole story on the scales.

And the reason I wanted to chat about this really

is because that 7,700 rule

gives people this false precision in both directions.

It makes them think they've gained more fat

than they have after a few big days,

and it sets up expectations around fat loss

that their body was never going to be able to meet,

regardless of what they did.

The scales can change much faster than body fat does,

and just knowing that hopefully helps you stop panicking

on a Monday morning,

and instead of going to extremes then

to quote unquote fix the damage,

you just make some good decisions

and carry on as you would have anyway.

And I think this is what I always say to people

when they have weekends like the one that I sort of talked about.

The most important decision is what you do next.

So just make a good one.

All right, guys, hopefully you followed along with that.

Let me know I'm on Instagram, Threads and X,

at Mikki Williden.

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Guys, you have a great week.

See you later.