In Defense of “Crash Dieting”

A “crash diet” is defined as “a way of losing body weight quickly by eating very little,” and nearly every YouTube doctor, social media influencer, and personal trainer will tell you this is the absolute worst way to lose weight.

Slash your calories too low and lose weight too fast, they warn, and you’ll burn muscle, “damage” your metabolism, and quickly regain all of the weight you lost.

Instead, they advocate a “slow and steady” approach: eat a little less, move a little more, and let weight loss occur as a side effect of a healthy lifestyle rather than as the explicit goal.

This approach can work, but it fails more often than not.¹²³⁴⁵

For many, “crash dieting” is superior to the “slow and steady” approach to fat loss.

Here’s why.

1. Crash Diets Are Usually Easier to Stick to than Gradual Weight Loss Diets

Whether you lose weight quickly or slowly, dieting is always unpleasant.

What makes it worth it?

Rapid, visible progress.

Compare these two scenarios:

Option A: You lose 1 pound per week for a year, and you’d rate your diet a 4/10 in terms of difficulty (hunger, cravings, sagging energy levels, etc.).

Option B: You lose 2 pounds per week for 6 months, and you’d rate your diet a 6/10 in terms of difficulty.

You lose weight twice as fast and diet half as long for only a moderate bump in difficulty.

Most studies show option B is the better choice.

For example, a study conducted by scientists at The University of Melbourne had 204 obese men and women follow a diet designed to help them lose 15% of their body weight—about 32 pounds on average.⁶

Half followed a diet that would help them reach their goal in 36 weeks, which entailed maintaining a 400–500 daily calorie deficit. The other half followed a crash diet designed to get them there in 12 weeks, eating just 450–800 calories per day.

The researchers counted the diet as successful if people lost at least 12.5% of their body weight, or about 27 pounds on average.

The result? Only 50% of the gradual weight loss group succeeded, compared with 81% of the crash diet group.

Despite losing weight three times faster, the crash diet group was about 60% more likely to reach its goal than the gradual weight loss group.

Another study conducted by scientists at The University of Sydney found similar results.⁷ Women assigned to a crash diet lost 34 pounds in 12 months, and were more likely to finish the study than women assigned to the gradual weight loss diet, who only lost 19 pounds. Specifically, 92% of the crash dieters finished the study, compared to only 77% of the gradual dieters.

The reason is simple: Results are the best motivation.

It’s much easier to put the fork down and push through cravings when the number on the scale is plummeting and you’re seeing changes in the mirror every week.

2. Crash Dieting Is Often Better for Maintaining Weight Loss

At this point you might be thinking, “Sure, crash dieting might be more motivating over a few weeks or months, but what about long-term maintenance? Don’t most of these people just gain all of the weight back and then some?”

No, actually, at least not any more than people who lose weight slowly.

While many people do rapidly regain weight after they stop dieting, most research shows that crash dieters maintain weight just as well if not better than people who lose weight slowly.

For example, in the same study from The University of Melbourne, the researchers checked in on the participants 3 years after they lost weight.⁸ While many of the people in both groups regained weight (always the case in weight loss studies), there was no difference between groups.

In other words, the people who lost weight quickly were able to maintain their weight loss just as effectively as the people who lost weight slowly. They weren’t more susceptible to “rebound.”

The same was true in the University of Sydney study: Three years later, 42% of the crash dieters had maintained their weight loss versus only 16% of the gradual dieters.⁹

Another study conducted by scientists at the Weight Control and Diabetes Research Center found that people who lost 2.2 pounds per week in the first two months of their diet were over twice as likely to maintain most of their weight loss after a year than those who lost 0.25 pounds per week.¹⁰

And another study from the University of Florida found that people who lost weight quickly were 5 times more likely to maintain their weight loss than people who tried to lose weight slowly.¹¹

In other words, people who “crash diet” are usually better at maintaining their weight loss than people who lose weight at a moderate pace.

3. Crash Diets Are Harder to Mess Up

Suppose you try to maintain a 300-calorie daily deficit. A little extra cream in your coffee, a few extra spoonfuls of yogurt, and a banana is all it takes to wipe out your deficit and stymie weight loss.

Now suppose your goal is to eat 800 calories per day but you accidentally overeat by 300 calories. Your calorie intake is still only 1,100 per day, which for most people is enough to lose 2+ pounds per week.

A miscalculation that completely stalls weight loss on a normal diet is now a rounding error.

Most people struggle to track their calories precisely enough to maintain a small to moderate calorie deficit, and crash dieting is often a more foolproof solution.¹²

5 Simple Steps to Effective Crash Dieting

Most people make three mistakes when crash dieting: not eating enough protein, not lifting weights or lifting weights improperly, and doing too much cardio.

This leads to muscle loss, unrelenting hunger and fatigue, and often binging.

Here’s how to avoid all of these problems.

1. Eat plenty of lean protein, some low-calorie vegetables, and almost nothing else.

This kind of diet is known as a protein-sparing modified fast (PSMF), and it’s basically a muscle-sparing crash diet.

You eat ~0.9–1.5 grams of protein per pound of lean body mass per day to preserve muscle mass, a few cups of low-calorie, filling vegetables like zucchini, broccoli, green beans, cauliflower, tomatoes, pickles, and asparagus to support digestion and stay satiated, and that’s it.

Generally speaking, if you’re over 30% body fat as a man or 40% body fat as a woman (obese), you should shoot for the lower end of this protein range (0.9 g/lb. of lean body mass). And if you’re under 15% body fat as a man or under 25% as a woman, you should shoot for the upper end of this range (1.5 g/lb. of lean body mass).

(Use this calculator to learn how much lean body mass you’re carrying).

Depending on your size and body fat percentage, this works out to around 100–250 grams of protein per day.

It’s also best to take a few supplements while following this diet:

• Protein powder, such as whey, casein, or plant protein, to make it easier to hit your protein target.
• A multivitamin to prevent micronutrient deficiencies.
• Fish oil for essential fatty acids.
• Potassium, from a supplement or low-sodium salt.
• Psyllium husk powder to improve satiety and digestion.

This helps you stay full for hours while adding only 20–30 calories to your daily total. I like to combine 5–10 grams of psyllium husk powder with plain non-fat skyr and a scoop or two of whey protein.

2. Try intermittent modified fasting.

Intermittent modified fasting (IMF) involves alternating between a few days of a protein-sparing modified fast with a few days of eating at maintenance. This allows you to create a massive weekly calorie deficit while only dieting a few days per week.

For example, a good starting place for a 300-pound man at 30% body fat would be something like 5 PSMF days and 2 maintenance days per week. A 150-pound woman at the same body fat percentage would want to do something more like 3 days of PSMF and 4 days of maintenance.

It’s also best to do your weightlifting workouts on your maintenance days, if possible.

Here’s a chart showing how much weight loss you can expect following this approach:

Note: This idea was popularized by the writer Lyle McDonald in his book, Intermittent Modified Fasting, which is worth reading for a more detailed explanation of this method.

3. Do 2–3 low-volume, high-intensity weightlifting workouts per week.

While crash dieting, you aren’t going to be able to gain a meaningful amount of muscle mass, so your only goal in the gym should be to maintain muscle.

Research shows that so long as you maintain the intensity (weight) of your workouts, you can massively slash your workout volume (sets) without losing muscle.

For example, one study conducted by scientists at the University of West Virginia found that people were able to maintain all of their muscle while eating just 800 calories per day and lifting weights three times per week.¹³ Another study from the University of Alabama at Birmingham found that weightlifters were able to maintain muscle mass with 1/9th of the volume it took to build it.¹⁴

A good rule of thumb is to do 2 full-body workouts per week, 1 set per muscle group per workout (yes, just 1), 4–8 reps per set, and to take each set 0–2 reps shy of failure. If you can add weight, go for it, but the goal is just to maintain the weight and reps you started with at the beginning of the crash diet.

Do that, and you won’t lose muscle.

4. Do very little cardio, if any.

Walk, do chores, play with your kids, and so on, but don’t bother with formal cardio if you don’t want to.

Compared to your already substantial calorie deficit, cardio won’t burn enough additional calories to meaningfully accelerate fat loss. What it will do is significantly increase fatigue, hurt your recovery, and make it harder to maintain the intensity of your weightlifting workouts.

If you want to do some cardio, keep the intensity very low (you should be able to easily talk) and don’t do more than 30–40 minutes at a time. Ideally, stick to low impact forms like cycling, swimming, rowing, and elliptical. Avoid anything longer or more intense than this.

5. Don’t crash diet for more than ~4 weeks at a time.

One of the reasons so many people quit crash diets is they don’t give the diet a clear end date. They go as long as they can until hunger, cravings, and fatigue forces them to tap out.

Instead, crash diet for a maximum of a few weeks, then raise your calories to maintenance for 1–2 weeks to recharge and reassess.

The more weight you have to lose, the longer you can crash diet before taking a break, but it’s still best not to stretch past 4 weeks.

For example, instead of crash dieting continuously for 12 weeks, it’s much better to crash diet for 3 weeks, go back to maintenance for a week, and then repeat twice more.

Keep in mind this is assuming you’re following the intermittent modified fasting approach, too, so you’re still including some days at maintenance each week. A full 6-week cycle of crash dieting might look something like this: