Like others said it’s technically possible, but why would you want to?

It very much depends on starting weight. Is it possible? Theoretically, yes. Is it safe? No, unlikely for most people.

20lbs or 9kg is a month is extreme weight loss. To lose 1kg of fat, you need a deficit of 7700kcals. For 9 kg that’s 69,300 kcals deficit needed over the month. Lets say thats over 28 days / 4 weeks: that’d be an average deficit of 2,475 kcals every day.

An average 30 year old man, who weighs say 80kg and average height.

• Basal Metabolic Rate (BMR) - 1750 kcal a day
• Total Daily Energy Expenditure (BMR x activity factor, lets say 1.2 assuming they are sedentary) - 2,100 kcal a day.

So they need 2100kcal a day just to stay as they are. If they did nothing else, the maximum possible deficit they could have is to eat nothing - but they’d only achieve 2100kcal deficit a day, and they’d not last very long.

For that person to lose 9kg in a month, they would realistically need to massively increase their exercise. Even if they increased their daily energy expenditure to 3,323 kcal a day (1.9 x BMR for a very active person), they’d then need to calorie restrict their diet to only 848 kcal a day to achieve the deficit. Even then a 848kcal intake is dangerously low intake and would require very careful management. And somehow that person would also need to have enough intake to feel able to do all that extra exercise.

It would put the body under extreme stress and be very difficult to maintain.

Now if the person was very severely obese - lets say 200kg - the BMR would be 2949kcal (it takes energy just to maintain the fat), and the TDEE would be about 3540kcal if sedentary (even doing nothing, they use more energy). In that situation, if they suddenly became very active, they could boost their TDEE to say 4000-4500 kcal, and would be able to eat 1690-2190kcal a day, and still have a 2475kcal a day deficit. They could lose the 9kg weight in a month. However it is not very realistic for a severely obese person to go from sedentary to extreme activity in such a short period, and maintain it, and while calorie restricting too.

So it could be done by an obese person, but it’s not realistic then and certainly not for anyone who is only overweight.

A big mistake people make when they try to lose weight is to try and fix the problem as fast as possible. But fast dieting leads to over exertion, over strenuous food restriction, failure and then despair. Even 1kg a week lose is a very high rate and difficult to sustain. Instead of trying to lose as much as possible in a month, it’s better to aim for a sustainable amount every week for a long time - such as 0.5kg. 6 months of sustained slow lose is generally much more successful and achievable than crash/fast/extreme diets that just fail over and over for 6 months. And generally when people do slow diets, they change habits and have a better chance of maintaining it.

If someone is actually considering a diet then the real key is: don’t make it a speed race, make it a marathon. Slightly reduce intake, slightly increase activity every day, and aim for a slow but steady loss. A 550kcal deficit every day is much much easier than trying to rush with 1100kcal deficit, and allows a sustainable lifestyle. For example the 80kg 30 year old person could do moderate exercise (e.g. 10,000 steps a day just walking), they could realistically consume 1900-2000kcal a day, maintain a 550kcal deficit each day and lose 0.5kg every week. In a month they’d lose 2kg, and in 4.5 months they’d lose 9kg.

The normal pace is 1 kg/week (~2lb), faster diet will lead to your body malforming, but it’s definitely possible.

Also exercise is not as important as proper diet. It’s better to do no exercise and eat little than burn many calories and eat even more.

Yes, and more. I dropped 40 pounds in about a month. Although it was due to extreme stress, so I don’t recommend that. But, it is physically possible, so there are other routes you can try.

You’ve probably heard it before, but the key to quick fat loss is dropping carbs, including beer. Sorry.

Track your carbs using a macro tracking app, because you don’t know how many carbs you are eating, you just don’t, and you’ll be surprised. Once you learn which foods are full of carbs, you can stop using the app, it’s just a learning tool, not something you need to keep doing.

Get it below 100g a day, and watch the fat burn away, and you’ll start feeling so much better, after the first couple of weeks. It can be a hard adjustment for some people, but it’s worth it.

Exercise is only about 20% of it, diet is 80%, which makes sense. It’s much easier to not consume the food in the first place, than to burn it off after it’s already fat.

However, to be healthy, not just lose fat, you need to do both diet and exercise. That’s why it’s always presented that way--“diet AND exercise”, not “diet OR exercise”.

It’s best to make the commitment to a permanent lifestyle change, rather than just aiming for a goal weight and then going back to drinking beer every day. You’ll QUICKLY gain the fat back, faster than you lost it, and that is disheartening.

If you just give up, you could end up with type 2 diabetes in 15 or 20 years, and that makes being old much worse. So, it’s worth the effort.

You can drop 20 pounds in a month, but you probably shouldn’t unless your overall size and weight make 20 pounds not as significant as it would be to the average human.

There’s a lot of serious illnesses/medical conditions that will make you loose a lot of weight, very fast. I think i.e some cancers are one of those.

They usually also kill you pretty quickly, but you didn’t ask for healthy.

This is more of a reminder - if you inexplicably loose a lot of weight, it’s not something to celebrate, but get checked up ASAP.

The first month, yes. In general that is not healthy to aim for. In general extreme programs are not healthy and not sustainable

At one point i used weight watchers to successfully lose a lot of weight - I lost 109 pounds over a couple years as planning for being better able to care for kids. This is a regular program, very much not extreme. However a key part of their program was weekly weigh-ins.

Their recommended intake varies by age, size and gender: I think I started at 2100 calories/day and was down to 1800 as I was reaching my goal. Meanwhile my ex’s target was 1200 calories/day

The programs goal was to lose about 2 pounds/week and focus on sustainable life changes - keeps you healthy with regular weight loss. However everyone had much bigger losses the first couple of weeks. I’m sure I lost more than 20 pounds my first month on the program, but it was water weight, not repeatable. Certainly not a healthy goal

Amputation

I am assuming your are in your 20s. When I was in my 20s I could loose five pounds in a week just be maintaining my excercise routine and diet.

If you can go five miles a day, than eat 1200 calories a day or less and stop drinking. You will shed 20 pounds in no time.

FYI: You didn’t say you wanted the plan to be healthy.

Of course you can, the question is should you?

If you don’t eat for a month you’d drop 10 kilos. But then you’d grow them back with interest.

Better to lose maximum 1 kilo (2 lbs) per month if you really want to lose it.

And yeah, beer isn’t the way forward for sure, except if you aim for a big belly and skinny legs…

Ditching all sugars is a good start IMO.

Good luck!

Stop drinking beer.

If you’re serious and your doctor thinks it’s fine (and you have some extra money) you can go on a glp-1 but even then a doctor wouldn’t recommend more than 2 lbs / week. I know people that have lost 10-15 lbs in the first few weeks so I’m sure it’s not out of the question. There are healthier ways to lose weight though.

Water fasting would be my best bet.

You can’t be in more caloric deficit and ketosis than by simply not eating.

Drink lots of water, to help with skin elasticity. Losing more than 3 lbs a week normally results in extra saggy skin.

Generally it’s best not to focus on losing weight but on adjusting calorie intake. Because muscle weighs more than fat, water weighs more than either, and the goal is generally to feel fit, not light.

When wrestling I used to do the “drop a kilo class” thing by bulking up in a way that could rapidly store water, then running to temporarily shed that water before weigh in, then immediately rehydrate up to the next weight class. That was usually around 10 lbs of weight, but I was dropping it and regaining within a 6 hour period.

Losing weight for health reasons isn’t going to be the same for everyone. Personally I find the best way for me to lose weight is to increase my metabolism, which I find I can do through endurance running in threshold temperatures. But for other people that just makes them tired and hungry without their metabolism adjusting. And without the metabolic change, you don’t get the added benefit of literally burning off stored energy.

Also, depleting fat cells isn’t the same as removing fat cells. Those cells are still there, and it’s going to take months for cellular change to happen in your body. So 20 lbs of weight loss in a month will mostly be loss of water, muscle, and energy stored in the fat cells. And as soon as you stop starving yourself, it’ll all come back. And that can happen in a matter of days.

I lost 15 pounds in March. I was eating an average of 1,100 calories per day.