Can I run a massive calorie deficit to lose weight while maintaining muscle as long as I get my protein?

backstory: I'd been trying and failing to do keto over the years as the diet is too strict for my bad habits. Then I heard several fitness authorities/influencers say to just track protein and stay within your calorie limit for the day. This is much easier for me to do. I'm 5'11" and about 230 lbs with about 32% bodyfat. I would like to lose at least 30 pounds of fat while maintaining or even increasing muscle mass.

So going by this, I could eat like 21 ounces of chicken breast to get about 180g of protein at around 1000 calories. Then I could just stop eating for the day or maybe have a few snacks? Would that work? Would I be losing muscle then or have too little energy?

  • To get bigger you need to get bigger. Dieting is contrary to the goal of putting on muscle.
    – Dude
    Feb 15 at 1:19

4 Answers 4


tl;dr - No, you can't.

I would like to point out the most relevant part of your question:

backstory: I'd been trying and failing to do keto over the years as the diet is too strict for my bad habits.

Given that, ANY "diet" that you try will fail in the long run. If you really want to lose the weight in a permanent fashion, then you need to correct the bad habits and make healthy eating the norm. The reason I put diet in quotes, is that any diet plan that relies on cutting different macros, eating 25 grapefruit a day or whatever is a short term, limited time effort. Once a specific goal is achieved, the bad habits take over and the weight goes up again.

Set short term, medium and long term goals. Don't overhaul your entire diet in a day, also set goals that you can achieve. Maybe this week it's limiting desserts to 3 days instead of 6, or substituting healthy desserts for ice cream with chocolate sauce. Success breeds success. Don't necessarily chase the scale, but let a mirror be your guide.

I would also point out that you likely didn't gain 50 extra pounds in a month, so trying to get rid of it in that same time is a recipe for failure (or extreme unhealth). Aim for a realistic reduction, such as 2-3 lbs a month. Yes, it will take you a couple of years to lose 50 lbs, but it will be healthy AND sustainable for the long term.

  • 4
    I overhauled and created several Wikipedia articles on diets (healthy ones and fad diets). The claim that "ANY diet that you try will fail in the long run" is baseless. There are diets that work, but not for everyone, to each their own. Of course OP's need to stick to the diet, this is the most important criterion for long term efficacy, but changing from a bad diet to a healthy diet IS still a diet and IS effective and even recommended (lookup the DASH diet and Mediterranean diet for examples - and Keto is great for epilepsy, not just weight management).
    – gaborous
    Feb 6 at 15:43
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    @gaborous I think answer makes clear that they mean "diet" in the sense of a temporary change in eating habits to lose weight. The word unfortunately has a lot of history of being used that way. Feb 6 at 18:35
  • I should have been more clear, especially since the word diet is a bit semantically overloaded to mean both short and long term. I meant it more in the long term sense. I'm not looking to "make weight" for anything in the short term. I'm looking for a lifetime diet aka long-term nutrition strategy that I can stick with, not be miserable and also help me reach my goals. Feb 7 at 1:31
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    @DanCsharpster - Your statement here and your question above are at odds with each other. You want to eat 1000 calories of protein and stop eating for the day. That is not a long term nutrition strategy.
    – JohnP
    Feb 7 at 13:55
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    @gaborous "Being an editor of many wikipedia article on diets": what does tell us this with respect to your qualifications to speak about nutrition? Additionally, the "There are diets that work, but not for everyone" is statistically undetermined, because "not everyone" can be read as "no one apart from one person", which is just statistical noise and does not tell us if a diet works or not.
    – EarlGrey
    Feb 9 at 10:46

These are called Protein-sparing modified fasts. It's an extraordinarily intense diet that is designed to minimize muscle loss while losing fat really fast. It's recommended to do it with a registered dietitian because it's not easy and there is a refeeding phase that you need to go through to make sure you don't blow back up. Also because of the exceedingly low calories, you'll not be able to get your micronutrients which can heavily impact your health even in the short term if you're not careful.

You will lose muscle mass. A significant portion of the dietary protein consumed will be used to keep you alive rather than maintaining muscle mass.

You won't have energy to do pretty much anything, much less do the training necessary to maintain or gain muscle.

A better long-term weight loss strategy is to do a far slower rate of loss. A much slighter caloric deficit with high protein and fiber intake. Aiming for around 1 pound to 1.5 pounds per week.

  • 3
    Great answer. I would add that the reason why muscle loss is nearly impossible to prevent with reduced calories diets is that carbs are necessary for muscles metabolism, so by reducing carbs, which is often required by calories reduction diets, it's very difficult to maintain muscles even with sufficient protein intake.
    – gaborous
    Feb 6 at 15:44
  • Last year I've been losing ~1 pound/week for 23 weeks in a row while gaining muscle. But I was going to the gym 6 weeks a week, so not just sitting around doing nothing. Feb 7 at 0:43
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    @JonathanReez Going to the gym 6 weeks per week is impressive! :)
    – reirab
    Feb 7 at 1:28

Yes, if you also go to the gym

In December 2022 my weight was at 178 lbs at a height of 5'11''. I've decided to lose weight and achieved it as follows:

  1. Cut down food consumption below 2000 calories, with no cheat days. Tracked all my food in Macrofactor and using kitchen scales to be accurate.
  2. Ate 150 grams of protein per day. For me this was in the form of 3 eggs and 3 whey protein drinks. The protein sources were ~700 calories a day, so I only had 1300 calories for my other meals.
  3. Took supplements like calcium, iron, magnesium, fish oil and others, to ensure I stay healthy despite the reduction in the amount of nutrients. You can lookup various lists of recommended supplements online, depending on your personal preferences and medical history.
  4. Ensured I walk at least 10 thousand steps per day.
  5. Worked out 6 days per week at the gym, focusing on strength exercises: bench press, deadlifts, squats and lots of other exercises. You can find many different programs online, depending on what equipment you have access to.

With this program I was able to get down to 155 lbs after 8 months of effort while gaining muscle, as evidenced by keeping logs of my lift performance at the gym.

However I still have to maintain this regime to this very day, the only difference being that my calorie intake is slightly higher to avoid losing further weight. And I won't lie: this is very, very hard. It takes up all my willpower to not fallback to my old habits and I can't promise you I won't be back to 178 lbs in a few years. I've thought it would get easier over time but unfortunately I'm still very much craving sugary foods, pizza and other "forbidden" snacks.

  • 2
    Unfortunately, lifting performance is not an indicator of muscle mass. Quite a bit of lifting performance boils down to improved activation of muscles. Small movements do not require full muscle mass, so the brain can be lazy and activate random muscle fibers without being too precise. When you go to make the same movement, it can activate different muscle fibers, so the mitochondria can respire. Only when you lift near your capacity is the brain forced to recruit most of your muscle fibers in a coordinated way. The first time you do this, it will be inefficient... Feb 7 at 4:18
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    It's pretty common knowledge that you can't lose weight and gain lean mass at the same time. Your account suggests that you can, and may set unrealistic expectations for other people who try it. I think it's great that you got health benefits, but I also think it's important that people don't attempt something that is infeasible and then blame themselves because it didn't work. I think it would be better for people to focus on their strength, like you did, rather than obsessing over their weight/lean mass. Feb 7 at 7:52
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    You didn't do a protein sparring fast which is what the OP was describing. You cut your calories to roughly 2000 a day and lost a pound a week while managing to maintain an active lifestyle. This means your TDEE on average is 2500 which is a little low but normal for an untrained individual at your height and weight.
    – DeeV
    Feb 7 at 14:41
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    OP: "Can I do X?" Answer: "Yes, anecdote: proceeds to tell a completely different story>". 2000 cal is not a "massive calorie deficit", and 8 months is not a sustainable period for living on 600g of chicken a day. A better formulation could be: "No, but you can take a less drastic, more manageable approach, for example here is what I did..."
    – njzk2
    Feb 8 at 17:31
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    @JonathanReez I'm not naysaying, I'm saying that your answer is misleading: your suggested regimen may or may not work, but you don't answer the question. "Can I lose weight and maintain muscle if I eat 1000kcal of chicken a day?". You answer "yes", but you show something else.
    – njzk2
    Feb 9 at 17:30

DeeV's answer should be the accepted (/EDIT: done by OP since then) and the most upvoted one. My answer here is only necessary to debunk the currently top voted answer, which unfortunately propagates a common misconception about diets, so please see it as a complement (with a few practical tips for OP near the end).

There is a common claim that most dieters will regain their weight or even more. This is blatantly false and comes from an old bogus study. Since then, it was shown by several systematic reviews and meta-analyses that long-term (2-5 years post diet), the weight loss persists, although with a rebound yes compared to the lowest, but the total weight remains lower than pre-diet, with estimates being an average of >3kg of weight loss and >3% of total weight loss 5 years post-diet (ref 1, ref 2).


Figure excerpt from this meta-analysis. Data from the Look AHEAD multicentric trials on diabetes and obesity management. The strict very low calories diet was enforced during the first 6 months, with gradual tapering off to higher calories the remaining of the 1st year, then off-site prescriptions of replacement meals and lifestyle changes such as physical exercise but little to no monitoring beyond the first year.

weight-loss-over-8-years Extended figure from the same data excerpt from here that goes up to 8 years after the start of the study (7 years post diet). Patients groups are segmented into 3 subfigures depending on their initial weight loss during the 1st year, and then into 4 line charts depending on their weight variation. Sadly, still no variability intervals, but the segmentation provides insights into the variability. We can still see that most dieters still kept some weight loss 7 years post diet.

From this figure, you will notice a few interesting facts: 1) all diets (that restrict calories intake) are correlated with long-term weight loss years post-diet, 2) exercise alone is ineffective for weight loss. These results are reproduced in loads of systematic reviews and meta-analyses on diets (I only picked here a few for conciseness, you can lookup on pubmed for more).

The latter may seem surprising, but it is in fact well known among obesity researchers, that dieting with calories restriction is much more effective and the primary treatment to reduce weight, and physical exercise only comes second to improve cardiometabolic function but not reduce weight (and weight reduction is the best predictor of long term improvement in metabolic disorders, including obesity but also diabetes and MASLD/NAFLD).

Very-low-energy-diets cause an impressive but temporary trough that does not last likely due to glycogen stores loss, which store water, so this trough is basically just water loss, not fat loss.

The best predictor for long term weight loss hence appears to be in several large studies such as the Look AHEAD trials not the diet itself, but rather adherence (ref 1, ref 2, ref 3). Recent evidence even suggest that it's not even adherence to the diet, but adherence to monitor and control one's own weight regularly that is the key to weight loss. Indeed, in a recent study, the researchers found that post-diet individuals who used a weight scale regularly to monitor their weight kept on average more weight off over the long term (ref1, ref2).

That said, depending on the type of diet you are doing, and the composition of macronutrients, this will have different effects on what you lose: if there is no protein in your diet, of course you will lose not just fat but also certainly some lean mass/muscles. On the other hand if there is enough proteins in your diet (not too much to avoid liver issues due to proteins poisoning), then you may be able to keep your lean mass, but without carbohydrates it will be near impossible to gain any new lean mass.

One last interesting note I remember is that even if you use a diet that is rich in proteins (but low calories or lacking carbohydrates, eg, ketogenic diet), studies found that physical exercise improves the chances of keeping lean mass. So if your goal is to keep your lean mass while losing weight, you definitely should consider physical exercise on top of dieting.

Another recent finding is that sleep appears to affect weight gain, with shorter sleep associated with weight regains at 1 year post diet (ref). It's also worth noting that the insulin and melatonin (sleep hormone) are tightly coupled since there are antagonistic receptors on the pancreas.

Finally, after you reached your weight goals, transitioning to a more balanced and sustainable healthy diet such as DASH or the mediterranean diet or vegetarian diet is highly recommended, as there are plenty of evidence that these 3 diets have cardiometabolic protection benefits, as the Dietary Guidelines for Americans 2020-2025 states (ref 1, ref 2). It is also important to know how to recognize and avoid dangerous fad diets, not all of them are dangerous, but the ones recommending to eat inedible items or to restrict whole types of nutrients are usually dangerous (only exception for the latter are allergies out of the top of my head).

Disclaimer: I significantly contributed to Wikipedia (in English) articles on metabolic disorders and diets using evidence-based medicine sources and I was attributed awards for my work on several of these articles (so I highly recommend you read those too of course! And the WHO materials too).

(PS: if link for this ref dies, use this doi instead).

  • Does that graph depict weight loss at the start of a new diet and how weight changes over two years? Or is it showing two years progress after a weight loss phase and people started eating more normally?
    – DeeV
    Feb 20 at 3:34
  • The graph has very little value, since it has no error bars and the curved lines are from some excel interpolation (i.e. they do not add any information), but thanks for providing the references. It may well be that the error (the spread of the values used to plot these points) makes invalid their point. Or not.
    – EarlGrey
    Feb 20 at 6:43
  • @EarlGrey While I agree that the figure would certainly benefit from showing variability ranges, "worthless" is too harsh given the data originate from the well established and regarded 2014 LOOK AHEAD multicenter trials on diabetes and obesity treatments. In the original you can find an extended figure showing the long-term trajectories segmented by the number of kg lost at year 1 and then subsequently, imho better than ranges, this should satisfy your curiosity.
    – gaborous
    Feb 20 at 15:11
  • @DeeV Great question, and the answer is kinda in the middle. This comes from 2014 intermediate results from the Look AHEAD multicentric study on diabetes and obesity management. The strict diet phase was done primarily under the first 6 months, with gradual increase in calories up to 1 year. Then after the first year, patients were prescribed to use replacement meals and other lifestyle interventions such as physical exercise, but were not monitored beyond that. This is the ISI protocol, more info here in the original paper.
    – gaborous
    Feb 20 at 15:22
  • It is a tad better, but it is limited to "Look AHEAD assessed the effects of intentional weight loss on cardiovascular morbidity and mortality in 5,145 overweight/obese adults with type 2 diabete". I am not sure consideration on people with type 2 diabete are representative of the general population (unfortunately it may be, in the near future).
    – EarlGrey
    Feb 20 at 16:42

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