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Two sentences, more than any others, are said to me in the consulting room.

“I kept restricting my food, and then the weight just stopped coming off.”

“I stopped dieting, and it all came straight back.”

In almost every case, neither sentence is a confession of weakness. Both describe something that body weight simply does. Weight has this property built into it, and you can see exactly why with arithmetic you already know.

Here is the conclusion, before the derivation:

The numerator is your habits. The denominator is a constant fixed by your age and sex. So:

Your weight is determined by your habits, your age, and your sex.

Put differently: a person who weighs 100 kg is living the habits that hold a body at 100 kg. Change the habits and the weight changes. Return to the old habits and the weight returns. That single sentence is the starting point of everything I do in weight management.

Part I — The derivation

1. Three equations nobody disputes

Basal metabolic rate (BMR) is the energy your body spends simply growing and maintaining itself — skin, fat, muscle, bone, and the internal organs. The bigger the frame and the organs, the larger the BMR.

Plants make this intuitive. A plant spends energy growing and maintaining its leaves, stem, roots and fruit, but it does not move. A plant’s “calories burned in activity” is zero, so all of its expenditure is basal. Human BMR is the same thing: the energy required to build and maintain the body itself.

K is BMR per kilogram of body weight (kcal per kg per day). Japan’s Ministry of Health, Labour and Welfare publishes it by age and sex in the Dietary Reference Intakes for Japanese (2025):

Basal metabolic rate per kg (kcal/kg/day) — Japanese reference values

Age	Men	Women
18–29	23.7	22.1
30–49	22.5	21.9
50–64	21.8	20.7
65–74	21.6	20.7
75+	21.5	20.7

Two things about K decide everything that follows. It is fixed by age and sex — no effort of yours moves it. And it falls with age. Hold on to that second point; it returns later with some force.

2. Folding the three into one

Substitute ② and ③ into ①:

There is a problem. The left side is in kilograms; the right side is in kilocalories. They cannot be equal as written. We need a conversion, and the conventional one is 1 g of body fat = 7 kcal, so 1 kg = 7,000 kcal. Written per day:

This is the central equation. Everything else falls out of it.

3. Why the loss keeps slowing down

Take someone who has just adopted a new set of habits. Assume calories eaten and calories burned in activity are now constant under those new habits — this is the whole point of a habit.

Month 1: 70 kg → 66 kg (4 kg lost). Write the equation over 30 days, using the average weight for the month (68 kg) to compute the basal term. Writing I for daily intake and A for daily activity calories:

Month 2: starting from 66 kg, suppose ΔW kg are lost. Same habits, so the average weight this month is 66 − ΔW/2:

Now subtract (B) from (A). Because the habits did not change, I and A cancel completely. Only the basal terms survive:

Solve for ΔW:

Now take the number 4 — last month’s loss — and rewrite it over the same denominator. Multiplying numerator and denominator by the same quantity changes nothing, so this is still just 4:

Put them side by side. Same denominator. The numerators differ by exactly 120K:

Keep the exact habits that took 4 kg off in month 1, and month 2 will take off less than 4 kg. Always. The arithmetic leaves no room.

The reason is plain once you see it. Weight went down, so the basal metabolic rate — which is K × weight — went down with it. Same food, same exercise, but the body now burns less. The deficit shrinks by itself.

Repeat the identical calculation for month 3, month 4, and so on:

Each month’s loss is smaller than the last, and never turns negative. ΔW converges to zero. The weight does not keep falling. It stops.

4. Where, exactly, does it stop?

Go back to the central equation and substitute the condition “weight has stopped changing” — that is, change in weight = 0:

Solve for weight:

Which is where we came in.

Notice what vanished: the 7,000. That conversion factor governs only how fast you converge. It has no influence whatsoever on where you converge. This is worth sitting with, because it means every argument about the exact energy density of fat tissue — and there are many — is an argument about the speed, not the destination.

The numerator is intake and activity: habits. The denominator is a constant set by age and sex. The claim is proved.

5. A worked example: cut 100 kcal a day

Halve the rice at dinner. Call it 100 kcal a day. Keep it up. What happens?

The naive prediction. 100 kcal × 365 days = 36,500 kcal. At 7,000 kcal per kg, that is 5.21 kg in the first year — and, presumably, another 5.21 kg the year after.

What actually happens. Nothing of the sort. As weight falls, BMR falls with it, and the whole thing converges. From the conclusion:

For a man aged 30–49 (Japanese reference weight 70.0 kg, K = 22.5, activity level 1.75), the honest answer is about −2.5 kg.

Roughly −2.2 kg by the end of the first year. And then, no matter how long you keep going, it never goes past −2.5 kg.

What cutting 100 kcal a day buys you is not “5 kg a year.” It is “a body 2.5 kg lighter, for the rest of your life.”

That is not a failure. It means a new weight has been defined by a new habit. Which is the entire point.

6. What the equation says about plateaus and rebound

Why am I not losing weight?

Because — the equation is blunt about this — your current habits match your current weight. The change has not gone far enough. You are still eating too much, or moving too little, or both.

But note carefully: the slowing itself is normal. A plateau is not failure. It is arrival — at the weight your habits specify. If you want to go lower, you must change the habits again. Not try harder at the same ones.

What rebound actually is

If habits determine weight, then the contrapositive is immediate: go back to the old habits and the weight goes back too.

That is rebound. Not weak will. Not a broken metabolism. Not a bad constitution. The equation simply reverted.

And here is the uncomfortable corollary. Reaching your goal weight and then “stopping the diet” is returning to the old habits. So the weight must come back. There is no version of this where it does not.

Where diets and drugs fit

There are effective weight-loss methods, and there are effective weight-loss drugs. In this framework, starting one of them is exactly one thing: adopting a new habit.

Which means there are precisely two ways to avoid rebound:

1. Continue the method or the treatment, indefinitely.
2. Stop only once you already have habits that hold the goal weight.

Someone going from 70 kg to 50 kg introduces a method capable of −20 kg, and in parallel rebuilds their habits, and stops only when habits that sustain 50 kg are genuinely in place. That is the only path. Everything else is a loan that gets called in.

Weight-loss treatment is not the destination. It is the runway.

Getting older on the same habits makes you heavier

Look at the table again. K falls with age. In the conclusion, a smaller denominator with the same numerator means a larger converged weight.

So it is not “I gained weight even though I eat the same as I always did.”

It is “I gained weight because I eat the same as I always did.”

7. The “speed up your metabolism” myth

Look once more at equation ③:

K is a constant set by age and sex. Therefore the only way to raise your BMR is to get heavier. And correspondingly, when a diet works and your weight falls, your BMR falls. It has to.

“Raise your metabolism to lose weight” does not survive contact with this equation.

So why does muscle still matter enormously?

Because you should not be thinking about weight. You should be thinking about volume.

One gram of fat occupies about 1.10 cm³. One gram of muscle occupies about 0.91 cm³. Replace 10 kg of fat with 10 kg of muscle and the scale does not move by a single kilogram — while the body visibly tightens, by roughly 17% in volume.

The real goal of weight loss was never the number on the scale. It is less fat and less volume. Which makes building muscle — or at minimum, not losing it — decisive. That requires protein at or above the recommended intake, and resistance training built into ordinary life. Both are in Part III.

Part II — Where this sits in the literature, and where it is wrong

Everything above is arithmetic a schoolchild can check. That is its whole value. But arithmetic that nobody has checked against the literature is just confident arithmetic, so here is the check.

Hall et al. reached the same conclusion — with calculus

In 2011, Kevin Hall and colleagues at the US National Institutes of Health published a dynamic mathematical model of adult human metabolism in The Lancet ²⁾. Their targets and their findings map almost exactly onto Part I.

They demolish the static rule — the “3,500 kcal per pound” rule, which says that a fixed daily deficit produces a steady, unending, linear weight loss. That rule had been written into official guidance by the NHS in the UK, the NIH and the American Dietetic Association in the US. It was derived by estimating the energy content of the tissue lost, and it ignores the fact that expenditure falls as the body shrinks — which is precisely the mechanism of Section 3 above.

What Hall’s model shows instead:

• Weight converges to a new steady state. Not endless linear loss — a plateau. (Sections 3 and 4.)
• A rule of thumb: for an average overweight adult, a permanent change of intake of 100 kJ per day (about 24 kcal) produces an eventual weight change of about 1 kg.
• It is slow. About half the total change arrives in the first year; about 95% takes around three years.

The last point deserves emphasis, because it is the one that rescues people. A 100 kg sedentary man who cuts 500 kcal a day settles at around 75 kg — but takes years to get there. The static rule predicts he loses 22 kg in the first year alone, and the resulting error can reach about 10 kg within that year. That gap between promise and reality is where most people conclude they have failed, and quit.

So: the arithmetic of Part I and the calculus of Hall agree on the shape of the answer. Weight converges, and it converges slowly. Nothing in Part I is original. It is a route to a known destination that a patient can walk unaided — which is the only thing I claim for it.

Where my equation is wrong

The numbers do not agree, and I would rather say so than have you find out.

	The equation above	Hall et al.
Cut 100 kcal/day → eventual loss	−2.5 kg	about −4 kg
Cut 500 kcal/day → eventual loss	−12.7 kg	about −25 kg (100 kg adult)
Half-life of the change	about 4 months	about 1 year

My equation under-predicts how much you can lose, and over-predicts how fast. Both errors have a single source, and it is worth naming precisely.

K is an average, and I used it as a marginal

K = 22.5 kcal/kg/day is a whole-body average: total basal expenditure divided by total body weight. But the tissues that make up that average are wildly unequal. Elia’s classic figures ³⁾, in kcal per kg per day:

Tissue	kcal/kg/day
Heart, kidneys	440
Brain	240
Liver	200
Skeletal muscle	13
Adipose tissue	4.5
Everything else	12

Now ask the question that actually matters: when you lose one kilogram, which kilogram is it?

Overwhelmingly, adipose tissue — at 4.5 — plus some skeletal muscle, at 13. Your heart, kidneys, brain and liver do not shrink. They are carrying the enormous coefficients, and they are not the tissue leaving.

So the metabolic cost of the marginal kilogram is far below the 22.5 average. My equation divides by a denominator that is too big. Therefore it predicts too little weight change. The direction of the error is not in doubt; only the size of it is, and for that you should use Hall’s empirical answer — about 24 kcal/kg/day for the average overweight adult, not my 39.

Which means: the fatter you are, the more wrong I am

The gap between the average and the marginal widens with adiposity. Hall’s finding is explicit: adults with more body fat lose more weight for the same intake change, and take longer to get there. Independent work confirms that Elia’s coefficients hold up in non-obese adults but require adjustment in the obese ⁴⁾.

So, honestly:

• Near a standard build, the equation works well. Its answer for a 100 kcal cut — about 2.5 kg — sits close to the figure published in Japan’s own dietary guidelines, which put the plateau at roughly 2 kg.
• In severe obesity, do not use it. For a 100 kg adult cutting 500 kcal a day it says −13 kg where Hall’s simulation says −25 kg. It will badly undersell what is achievable, and that is the last thing anyone in that position needs to hear.

One caution in the other direction, for completeness. Hall’s simulations assume the intake cut is actually sustained. In reality it rarely is: weight loss drives a compensatory rise in appetite of roughly 100 kcal per day for every kilogram lost ⁵⁾. Real-world results therefore tend to land below the model’s ceiling — not because the person is weak, but because the biology is pulling in the other direction the whole way down.

What survives

Every number above can move. The structure cannot:

• Weight converges. It does not fall forever.
• The destination is set by habits, age and sex.
• A plateau is not failure.
• Rebound is the equation reverting, not a character flaw.

Whatever value you put in the denominator, convergence is preserved. That is the part I would defend anywhere.

Part III — What to actually do

If you weigh 70 kg and want to weigh 50 kg, there is exactly one task: acquire the habits of a person who weighs 50 kg. Here is what I ask patients to do.

1. Make it a hobby

The moment it becomes a penance or a quota, it is over — and a thing you do not continue is not, by definition, a habit. This is not motivational fluff; it is a technical requirement. Part I showed that reaching the new weight takes years. A method you cannot sustain for years is not a method. Treat the falling number as the day’s small pleasure. Picture, concretely, the version of you at the other end.

2. Weigh yourself daily — and read the trend, not the day

Step on the scale after your bath, every day, and record it. Look at the graph, not the number.

Weight behaves like a stock price. A 0.5 kg jump overnight is completely ordinary and is almost entirely water. Judging yourself on a single day’s reading is judging yourself on noise.

Get a scale that records automatically. Manual entry fails, far faster than anyone expects. A smartphone-linked scale logs the moment you stand on it. This single choice has an outsized effect on whether you are still doing this in six months — treat it as the investment that turns the habit into “just stand there.”

3. Movement — build it into the life you already have

What the guidelines say. Japan’s national physical activity guide (2023) recommends, for adults: 60+ minutes daily of walking or equivalent — about 8,000+ steps; resistance training 2–3 days a week; and avoid long unbroken sitting. For older adults, about 6,000 steps.

What I actually say. Nobody goes from a standing start to 8,000 steps and stays there. So: put the floor at 5,000 steps, hold it, then walk it up toward 8,000. A target you abandon never becomes a habit, and a habit is the only thing that moves the numerator.

Do the resistance training. Section 7 explained why: the goal is volume, not the scale. Lose muscle and the weight falls while the body stays soft.

Do not try to find time to exercise. Carving out a new hour is how people quit in week three. Convert what you already do:

• On a fine morning, get up an hour early and walk for 30 minutes.
• Swap the car commute for the train.
• On the way home, walk one, two, three stops — and get on the train when you have had enough.
• Take the stairs as far as you can, then take the lift the rest of the way.

Deciding in advance that you are allowed to stop partway is what makes it survive. (Cycling on flat ground, incidentally, is excellent transport and mediocre exercise. Do not count on it.)

4. Meal timing — leave a gap

This is the highest-yield item on the list.

Body fat is only mobilised for energy once the supply of glucose runs out. Put the other way round: while you keep eating, your fat is never called upon. Hence the gap between meals matters.

What I suggest is a gap of 15 hours or more, once a day:

Skipping breakfast may feel wrong. But “three proper meals a day” is not automatically optimal for someone trying to lose weight. During a weight-loss phase, securing a genuine gap is the more coherent strategy.

“Hungrier is better” is false. A genuine gap helps. Extreme fasting is counterproductive. Run short of both energy and protein for long enough and the body will break down muscle to make up the difference — at which point your volume does not fall, and the mirror does not change. Hunger that brings dizziness, loss of concentration, or feeling unwell has gone too far. That is a signal, not a score.

5. Nutrition — cut carbohydrate, protect protein

Carbohydrate. Until you reach your goal weight, keep it low. Rice, bread, noodles — and sugared drinks, which are the easiest large win most people have available.

Protein is not negotiable. This is the one line you do not cut. Japan’s 2025 dietary reference intakes recommend:

Recommended protein intake (g/day)

Age	Men	Women
18–49	65	50
50–64	65	50
65+	60	50

While losing weight, do not go below this. Diet without enough protein and the body takes the deficit out of muscle rather than fat — which defeats the entire purpose.

Protein content of common foods

Food	Portion	Protein
Chicken breast, skinless	100 g	~23 g
Beef or pork, lean	100 g	~20 g
Fish (salmon, mackerel)	1 fillet (80 g)	~18 g
Firm tofu	150 g	~10 g
Natto	1 pack (50 g)	~8 g
Egg	1	~6 g
Milk	200 ml	~7 g

A chicken breast, a fillet of fish, two eggs and a pack of natto comes to roughly 62 g. Add tofu or milk and a man clears the recommendation.

Water. Eat less and you also drink less, because a surprising share of your fluid comes from food. Drink calorie-free fluids deliberately.

Vitamins. Eat less and you get fewer vitamins. A multivitamin covers the gap cheaply.

6. When you are going to eat anyway

Not a moral failure — a choice to be made well.

• Choose the protein-heavy option — grilled meat, yakitori, fish, eggs.
• If it must be a rice bowl — small rice, extra meat on the side, an egg on top.
• If it must be ramen — leave as much of the noodle as you can, and load it with pork and egg.

The principle never changes: take out carbohydrate, put in protein.

7. An occasional large meal is genuinely fine

This follows directly from Part I, and it matters more than it looks.

Weight is determined by habits. Turn that over: a one-off act, which is not a habit, does not determine your weight.

Suppose one day you eat 2,100 kcal more than you should. At 7 kcal per gram of fat, that is 300 g. And as long as it does not become a habit, the weight drifts back to whatever your habits specify.

A single big meal does not erase months of work. The thing to watch is never the day. It is the habit.

8. If you drink

Choose distilled spirits — a highball is the easy default. Beer, sake and sweet cocktails carry substantially more sugar.

One caveat, and it is the one people dodge: a low number on the label means nothing if the volume goes up. “It’s zero-sugar” is not a licence for a fourth one.

Separately from weight, alcohol affects blood pressure, cardiac arrhythmia and the liver. If you can drink less, drink less.

9. Think back to when you were thinner

The thinner version of you was, almost certainly, someone who:

• spent far more hours of the day hungry,
• had less money in their wallet,
• and went to the convenience store far less often.

Weight is set by habits — so recover those habits and you recover that weight. Concretely: keep carbohydrate out of arm’s reach and stop snacking; do not carry much cash; stay out of the convenience store.

The point is not to summon more willpower. It is to reduce the number of moments in which your willpower is tested. That is the whole trick, and it is why it works.

10. Ageing on the same habits makes you heavier

K falls with age. Smaller denominator, same numerator, larger converged weight. So unless you eat progressively less as you age, you will gain — with certainty. Not “despite eating as I always did.” Because of it.

11. When the weight will not move

The equation is unsentimental: the change in habits is not yet sufficient. Still eating too much, still moving too little, or both.

But — again — the slowing is normal. Weight converges; it does not fall forever. A plateau means you have approached the weight your habits define. To go lower, change the habits another notch.

One exception worth knowing. Rapid or unexplained weight change, in either direction, can indicate an underlying condition — thyroid dysfunction among others. If the numbers do not match the behaviour, that is worth investigating with a doctor rather than pushing harder.

12. If changing how you eat is genuinely beyond you right now

Some people read all of the above and know, honestly, that they cannot execute it. That is a legitimate position, and medicine has something to offer.

GLP-1 receptor agonists are now well established for weight management in people with obesity. They are prescription medicines with real side effects, real costs, and real variation in response between individuals — they require a doctor, and they require assessment of whether they are appropriate for you. What I can offer here is not a recommendation but a framing, and it is the same framing as everything else in this article:

Starting a drug is adopting a new habit. Nothing more mysterious than that. Which means Part I’s conclusion applies without modification: stop the drug, return to the old habits, and the weight returns. The equation does not care why the numerator changed.

So the treatment is worth doing when it is used as it should be: alongside a rebuild of the habits, with the goal of stopping only once habits that hold the target weight are actually in place.

The drug is not the destination. It is the runway.

13. Rebound, one last time

“Weight is determined by habits, age and sex” means, with no wriggle room, “return to the old habits and the weight returns.”

That is all rebound has ever been. Not willpower. Not your constitution. The equation reverted.

So: acquire habits that hold the goal weight, and only then finish the diet.

The goal of a diet was never reaching the target weight. It is owning the habits that keep you there.

Summary

If your weight is not what you want it to be, the thing to change is not the weight. It is the habits. Live as the person at your goal weight lives. Stripped to its core, dieting is nothing but that.

Limits of this article

• It does not apply to severe obesity or severe underweight. The reference values used are drawn from populations of standard build. See Part II.
• Basal metabolic rate varies between individuals. This is an approximation built on population averages, and guarantees nothing about any one person.
• Conditions affecting metabolism change the premises — thyroid disease among them. Rapid weight change should prompt investigation, not effort.
• Short-term weight swings are largely water and glycogen, and cannot be read as changes in fat.
• 1 g of body fat = 7 kcal is an approximation. Adipose tissue contains water and other components.

福本医院は大阪市中央区南船場にある内科・循環器内科です。
大阪メトロ御堂筋線・心斎橋駅から徒歩2分、なんば（難波）からは1駅です。長堀橋・本町・四ツ橋からも徒歩圏内で、新町・堀江・立売堀をはじめ大阪市西区からも多くの患者様にご来院いただいております。

■ この記事のポイント

本記事は「ダイエット論 ― 体重は生活習慣と年齢と性別で決まる」の
続編にあたる、実践編です。理論編で導いた結論を、日々の生活にどう
落とし込むかをご説明します。

・体重は「生活習慣 ÷ 年齢と性別で決まる定数」で決まります
・食事の間隔を1日15時間以上空けることが、最も効きます
・タンパク質は削らない（男性65g・女性50g／日）
・停滞は失敗ではなく、その生活習慣で決まる体重に近づいたということです
・リバウンドは意志の問題ではありません。元の生活習慣に戻れば体重も戻ります

70kgの方が50kgになりたいのであれば、やるべきことは一つです。「50kgを維持できる生活習慣」を身につける。 ここから先は、そのために当院が実際にお勧めしている方法です。

理論の裏づけ（なぜ痩せなくなるのか、なぜリバウンドするのか）を先に
お知りになりたい方は、理論編をご覧ください。

 

【動画でご覧になりたい方へ】
同じ内容を動画でも公開しています。

1. まず、ダイエットを「趣味」にする

苦行やノルマだと思った時点で、まず続きません。そして続かないものは、定義上、生活習慣にはなりません。

体重が減っていくことを、毎日の楽しみとして扱う。ダイエットに成功したご自身を、具体的に思い描いてみてください。

これは精神論ではありません。「継続できる形にする」という、技術的な要請です。理論編で示したとおり、新しい体重に到達するには年単位の時間がかかります。続かない方法には、そもそも意味がないのです。

2. 体重測定 ― 毎日測り、トレンドで見る

毎日お風呂上がりに体重計に乗り、記録する。グラフで評価する習慣をつけましょう。

大事なのは、その日の数値で一喜一憂しないことです。体重の動きは株価によく似ています。日々の上下ではなく、トレンド（傾向）で判断してください。1日で0.5kg増えることは普通にあります。それはほぼ水分です。

自動で記録される体重計を

手入力は、想像以上に続きません。スマートフォン連携に対応した体重計なら、乗るだけで自動的にアプリへ記録されます。

選ぶときは、通販サイトや検索エンジンで 「体組成計 スマホ連携」 と検索してみてください。iPhoneをお使いなら 「体組成計 ヘルスケア 連携」、Androidなら 「体組成計 Google Fit 連携」 と加えると、より絞り込めます。

確認すべきは、次の3点だけです。

• スマートフォンのアプリに、自動で記録されること
• お使いのスマートフォン（iPhone／Android）に対応していること
• 体重に加えて、体脂肪率が測れること

価格帯は幅がありますが、この3点を満たしていれば十分です。体重計選びは、じつは成否をかなり左右します。「乗るだけ」にするための投資だとお考えください。

3. 運動 ― 生活のなかに組み込む

国が推奨している量

厚生労働省「健康づくりのための身体活動・運動ガイド2023」では、成人について次のように推奨されています。

当院がお伝えしていること

とはいえ、いきなり8,000歩は続きません。続かない目標は、生活習慣になりません。

ですので当院では、まず1日5,000歩を最低ラインに置いていただき、そこから8,000歩へ近づけていくことをお勧めしています。スマートフォンのアプリ（iPhoneなら「ヘルスケア」）で、毎日の歩数を確認してください。

筋力トレーニング週2〜3日は、ぜひ取り入れてください。理由は理論編で述べたとおりです。ダイエットの目的は体重計の数字ではなく、身体の体積を減らすこと。筋肉が落ちれば、体重が減っても身体は締まりません。

「運動の時間」を作ろうとしない

時間を新たに確保しようとすると、挫折します。すでにある行動を、運動に変えてください。

• 天気の良い朝、1時間早起きして30分散歩する
• 車通勤を電車通勤に変える
• 通勤・通学の帰りに、1駅〜3駅、歩けるだけ歩く（途中から電車やバスに乗ればいい）
• マンションやビルでは、階段を昇れるだけ昇る（途中の階からエレベーターに乗ればいい）

「全部やらなくていい、途中まででいい」と決めておくと、続きます。

なお、平地での自転車は、あまり良い運動にはなりません。移動手段としては優秀ですが、運動量としては期待しないでください。

有酸素運動とは？｜「会話できる強さ」が健康の秘訣｜心不全・生活習慣病・ダイエットへの効果を解説

4. 食事習慣 ― 食事の間隔を空ける

ここが最も効きます。

体脂肪は、糖の供給が途切れて初めて、エネルギーとして使われ始めます。逆に言えば、何かを食べ続けている限り、体脂肪の出番はありません。ですから食事と食事の間隔を空けることが重要になります。

当院がお勧めしているのは、1日15時間以上、食事の間隔を空ける形です。

朝食を抜くことに抵抗を感じられるかもしれませんが、「3食きちんと」は、減量を目指す方にとって最適解とは限りません。減量期においては、空腹の時間を確保するほうが理にかなっています。

【必ずお読みください】この方法が適さない方

以下に当てはまる方は、自己判断で行わず、必ず主治医にご相談ください。低血糖などの危険があります。

• 糖尿病で治療中の方（特にインスリン、SU薬を使用中の方）
• その他、低血糖を起こしうるお薬を使用中の方
• 妊娠中・授乳中の方
• 高齢の方、痩せている方、体力の落ちている方
• 摂食障害の既往がある方
• 成長期のお子さま

「空腹であればあるほど良い」ではありません。
空腹の時間を確保することは有効ですが、極端な絶食は逆効果です。エネルギーもタンパク質も不足した状態が続くと、身体は筋肉を分解してエネルギーに変えます。筋肉が落ちれば身体の体積は減らず、見た目も締まりません。ふらつき、集中力の低下、体調不良が出るような空腹は、行き過ぎです。

5. 栄養 ― 炭水化物を控え、タンパク質を守る

炭水化物

目標体重に達するまでは、炭水化物を極力控えましょう。ご飯、パン、麺、そして砂糖入りの飲料です。

タンパク質は「削らない」

ここは削ってはいけない項目です。厚生労働省「日本人の食事摂取基準（2025年版）」における、タンパク質の推奨量は次のとおりです。

タンパク質の推奨量（g/日）

年齢	男性	女性
18〜49歳	65	50
50〜64歳	65	50
65歳以上	60	50

減量中こそ、この量を下回らないようにしてください。タンパク質が不足したまま減量すると、身体は脂肪ではなく筋肉を削ります。

タンパク質を多く含む食品

食品	目安量	タンパク質
鶏むね肉（皮なし）	100 g	約 23 g
サラダチキン	1個（110 g）	約 24 g
牛肉・豚肉（赤身）	100 g	約 20 g
魚（鮭・さばなど）	1切れ（80 g）	約 18 g
木綿豆腐	1/2丁（150 g）	約 10 g
納豆	1パック（50 g）	約 8 g
卵	1個	約 6 g
牛乳	200 ml	約 7 g

たとえば、サラダチキン1個＋魚1切れ＋卵2個＋納豆1パックで、およそ 62g。ここに豆腐か牛乳を足せば、男性の推奨量にも届きます。

水分とビタミン

• 水分：食事量が減ると、食事から摂っていた水分も減ります。ノンカロリーの水分をしっかり摂ってください。
• ビタミン：食事量が減ればビタミンも不足します。マルチビタミンのサプリメントで補いましょう。

6. どうしても食べたいときは

我慢しきれないときの、現実的な選び方です。

• タンパク質の多いものを選ぶ ― 焼肉、焼き鳥、魚料理、卵料理
• どうしても牛丼なら ― 小盛り＋牛皿＋温玉のせ（ご飯を減らし、タンパク質を足す）
• どうしてもラーメンなら ― 麺をできるだけ残し、チャーシューと味付け卵をトッピング

考え方はどれも同じです。炭水化物を減らし、タンパク質に置き換える。

7. たまになら、しっかり食べても大丈夫です

これは「ダイエット論」から直接導かれる、重要な帰結です。

体重は生活習慣で決まります。裏返せば、習慣でない一度きりの行動は、体重を決めません。

仮にある日、2,100kcal 余計に食べてしまったとします。体脂肪1g＝7kcal ですから、増えるのは300gだけです。そしてそれが習慣でない限り、体重はやがて今の習慣で決まる体重へ戻っていきます。

一度の食べ過ぎで、これまでの努力が消えることはありません。気にすべきは1日ではなく、習慣です。

8. お酒を飲むなら

蒸留酒を選んでください。特にハイボールがお勧めです。ビール、日本酒、甘いカクテルは糖質が多くなります。

ただし一点。表示カロリーが低くても、量を飲めば同じことです。「糖質ゼロだから」と本数が増えては、意味がありません。

なお、飲酒は体重とは別に、血圧・不整脈・肝臓への影響もあります。減らせるのであれば、減らすに越したことはありません。

お酒は太る？純アルコール量と脂肪肝（MASLD・MetALD）の関係

9. 「昔、痩せていた頃」を思い出してみてください

痩せていた頃のご自身は、おそらくこうだったはずです。

• 空腹を感じている時間が、今よりずっと長かった
• 財布の中のお金が、今より少なかった
• コンビニに、今ほど行かなかった

体重は生活習慣で決まるのですから、その頃の生活習慣を取り戻せば、その頃の体重に戻ります。具体的には——

• 身の回りに炭水化物を置かない。間食をしない
• 財布にお金をあまり入れておかない
• コンビニには極力行かない

意志の力に頼るのではなく、意志を試される場面そのものを減らす。これが続けるコツです。

10. 歳を取ると、同じ生活では太ります

理論編の式を思い出してください。分母の基礎代謝基準値は、年齢とともに下がります。

分母が小さくなるということは、同じ分子（同じ生活習慣）なら、収束する体重は大きくなるということです。

つまり、歳を取る分だけ食べる量を減らしていかないと、必ず太ります。「昔と同じように食べているのに太った」のではなく、「昔と同じように食べているから太った」のです。

11. 体重がなかなか減らないときは

厳しいようですが、式はこう言っています。

生活習慣の改善が、まだ不十分です。

現状では、食べ過ぎか、運動不足か、その両方ということになります。

ただし、減り方が鈍ること自体は正常です。理論編で示したとおり、体重は減り続けるのではなく、ある一点へ収束していきます。停滞は失敗ではなく、その生活習慣で決まる体重に近づいたということです。さらに減らしたいのであれば、生活習慣をもう一段変える必要があります。

なお、急激な体重の増減や、生活習慣で説明のつかない変化がある場合は、甲状腺機能異常などの疾患が隠れていることもあります。気になる場合はご相談ください。

健康診断の受け方と結果票の見方｜健診の流れ・A〜F判定・血液検査・「要再検査」と言われたら【大阪・心斎橋 福本医院】

12. 食事習慣を変えるのが難しい方へ

ここまでお読みになって、「食事習慣を変えるのが、どうしても難しい」と感じられた方もおられると思います。

当院では、そうした方を対象に、自由診療（保険適用外）による減量治療を行っています。

ただし、これは「新しい生活習慣を一つ取り入れる」ことにほかなりません。理論編で示したとおり、治療をやめて元の生活習慣に戻れば、体重も元に戻ります。

ですから当院では、治療と並行して生活習慣を改善していただき、目標体重を維持できる習慣が身についた時点で終了するという進め方をお勧めしています。治療は目的ではなく、生活習慣が変わるまでの助走です。

なお、糖尿病の治療（保険診療）とは、対象も目的も異なります。糖尿病の治療については、別途ご相談ください。

13. リバウンドとは何か

もう一度だけ、確認します。

「体重は、生活習慣と年齢と性別で決まる」ということは、「元の生活習慣に戻れば、体重も元に戻る」ということです。

これがリバウンドです。意志の問題でも、体質の問題でもありません。式が元に戻っただけです。

リバウンドしないために

目標体重を維持できる新しい生活習慣を身につけてから、
ダイエットを終了する。

これが決定的に重要です。ダイエットのゴールは「目標体重に到達すること」ではありません。「目標体重を維持できる生活習慣が定着すること」です。

まとめ

体重の増加は、高血圧・脂質異常症・糖尿病といった生活習慣病、さらには心不全のリスクに直結します。減量についてお困りのことがあれば、どうぞ当院にご相談ください。

理論的な裏づけを詳しくお知りになりたい方は、「ダイエット論 ― 体重は生活習慣と年齢と性別で決まる」をご覧ください。