Aggressive diets have a bad reputation in the nutrition world.
There are many reasons for this. A lot of these reasons are valid reasons too.
But something that a lot of people struggle with when it comes to nutrition is nuance.
Something can be a bad idea for most people, while also being a good idea for some people.
If you think in black and white terms, you will likely conclude that nobody should ever attempt relatively fast weight loss.
Instead, with this post, I want to look at it from the other perspective.
Most people should not be aiming for quick weight loss. But there are some exceptions. I want to discuss this perspective in a balanced fashion.
Defining “Aggressive Dieting”
Aggressive dieting does not really have a definition. The general concept just involves aiming for relatively quick weight loss.
As a simplified rule, I would define aiming for >1kg per week weight loss, for multiple weeks in a row, as aggressive dieting.
But this simplified rule falls apart at extremes. A shorter, 60kg female wanting to drop to 54kg in 7 weeks technically would not fit into that rule. But I would deem that to be aggressive.
A 160kg person looking to drop to 149kg in 10 weeks would fit within that rule, but I would not consider that to be as aggressive as the previously mentioned example.
Because of that, I would define aggressive dieting as either of the following:
- Aiming to lose >1.5% of body weight per week, for multiple weeks.
- Aiming for a calorie intake that is <60% of the calories required to maintain your weight.
Meeting either of those criteria would be classified as aggressive dieting by me. It covers a broad range of situations.
This is my personal definition, not a consensus amongst researchers or anything.
Downsides of Aggressive Dieting
There are a lot of downsides to aggressive dieting. Keeping it brief, I will use dot points.
- Increased hunger. This can be complex though. Sometimes going quite low calories reduces hunger.
- Increased restriction. It is hard to be flexible on a strict approach, or with a limited calorie budget.
- Increased risk of muscle loss. Although if protein intake is high and resistance training is involved, muscle retention is often better than you would expect.
- Potential increased risk of disordered eating.
- Difficulty adhering to the plan.
- Harder to get a good amount of micronutrients from food. This can be partly covered with supplementation, but there are still beneficial components of food that can be missed.
- Reduced enjoyment of food and social situations.
- Decreased performance in training and competitions, if relevant.
- Low energy availability and downregulation of certain processes of the body.
The list can go on for a long time.
Potential Benefits of Aggressive Dieting
This list is much briefer.
It basically comes down to two things:
- Time
- Adherence (in some cases)
The time aspect is easy to understand. Losing 1.5% of body weight per week would get you to where you want to be 3x faster than 0.5% per week would. That can be appealing.
The adherence part is a bit more confusing without context.
Time commitment is a component of that. For some people, it is easier to push hard for shorter periods of time than it is to push moderately for an extended timeframe.
Losing 8kg in 6 weeks would involve 6 weeks of hard work. At 1/3 of that rate, it would take 18 weeks.
Some people find it easier to make large changes for 6 weeks than to make moderate changes for 18 weeks.
Another component is that some people like a challenge. They might like the appeal of an approach that is difficult or significantly different to their normal approach.
Does Slow and Steady Weight Loss Reduce the Likelihood of Weight Regain?
It is a common assumption that quick weight loss also leads to a high likelihood of quick regain.
Is that what the research shows though?
I think a lot of people observationally believe this line because:
- They have heard others say it.
- Habits are important in maintaining weight loss.
- We have seen a lot of people lose weight quickly and then regain weight.
How often do you see people lose weight slowly and maintain that weight loss though?
The research shows that MOST people who lose weight, regain weight.
It is hard to build a case that slow weight loss has a high success rate either.
There is not much research directly comparing rates of weight loss and outcomes.
My interpretation of the research is that weight loss maintenance rates are a little bit better in those who lose at more moderate rates. But it is not as big of a difference as you would think.
It is also worth acknowledging that the habits required to be in a moderate calorie deficit are different to the habits required at maintenance calories.
When you end a fat loss phase, you need to make changes to go to maintenance calories. This could be an intentional change or an unintentional change.
The only exception would be if you went so slow or for so long that your deficit calories became your maintenance calories. But this is incredibly rare.
You likely want to keep relatively similar habits to what you did during the fat loss phase. But there will almost always needs to be differences.
Weight-loss maintenance has less to do with what you do during the weight loss phase, and more to do with what you do AFTER the weight loss.
Details to Ideally Have in Place Prior to an Aggressive Diet
There are a few things somebody should have in place prior to undertaking an aggressive diet. These are not rules, but they would be ideal.
The first one is to have a good relationship with food.
Jumping into a restrictive approach is not a recipe for building a good relationship with food. It is likely to worsen it. Having a good relationship with food at the baseline helps for having a good foundation.
There also should be no form of binge eating or disordered eating. Aggressive dieting is highly likely to exacerbate these things.
Ideally, you should also have blood test done looking for nutrient deficiencies. These should be addressed prior to significantly reducing calorie intake.
A final thing that would be incredibly beneficial would be to have a track record of consistency with nutrition.
If you have stuck to the approach you want to stick to consistently, it improves the likelihood of having a good outcome.
If you are already struggling with adherence and consistency, does it make sense to make things harder?
Situations Where It Can Make Sense
There are a few situations where aggressive weight loss can make sense. I will try to go through them individually. I am sure there will be situations that I miss. My goal is just to cover some common ones.
Quick Weight Loss Prior to Bariatric Surgery
For those who have decided to undergo bariatric surgery, the gold standard protocol is to undergo a very low-calorie diet (VLCD) for 2-4 weeks prior to the surgery.
This typically involves 600-1000kcal per day. Often it is done with meal replacement shakes such as Optifast or Formulite. But there are many ways of doing it.
The reason this is often performed is to reduce the size of the liver prior to surgery.
2-4 weeks on a VLCD can reduce the size of their liver by up to 20%. This can make theoretically make surgery easier and safer.
People undergoing bariatric surgery have generally already tried many approaches to weight loss.
Aiming for slow to moderate weight loss to achieve this reduction in liver size would have an incredibly low success rate. Undertaking a VLCD for 2-4 weeks does not have a perfect success rate, but it is high enough to reduce liver size in almost all cases.
Post-Bariatric Surgery for an Extended Period
Following bariatric surgery, most people will be losing weight at a fast rate for the first 6-12 months.
They will also be consuming <60% of their maintenance calories.
This fits the criteria of aggressive dieting.
The first year or so is an important phase though. Research indicates that early post-operative weight-loss is predictive of maximal weight-loss outcomes.
Research indicates that multiple years after the surgery, on average people are regaining weight.
Losing more weight initially helps give a lower baseline prior to weight regain. And if they never lost that weight in the first place, would they have still been gaining from a higher baseline?
Of course, the goal is weight maintenance at the end. And many people achieve that.
That becomes a separate conversation. Bariatric surgery itself is a specific topic. I am just highlighting that somebody who has undergone that surgery likely benefits more from a relatively aggressive rate of weight loss than from trying to slow it down.
Quick Weight-Loss Prior to Knee/Hip Surgery to Meet Requirements
A lot of surgeons set weight targets for their patients to meet prior to surgery.
This is partly because of the belief that lower body weight could increase the likelihood of a good long-term outcome.
But it does create a challenge for some people.
Imagine being heavily burdened by knee pain. This would impact day-to-day life as well as the ability to exercise. Then imagine being told by your surgeon that they will not operate until you lose 10-15kg.
Would you want to lose that weight fast or slow?
Doing it slow delays how long it is until you are eligible for surgery. It prolongs how long you are in pain for.
You can see an argument for somebody wanting to achieve that goal quicker if they could.
Bodybuilding and Mini-Cuts
A lot of bodybuilders do mini cuts. This involves being in a large calorie deficit for 3-6 weeks.
Bodybuilders are striving to improve their body composition by building muscle and losing fat. It is hard to build muscle in a calorie deficit. It is borderline impossible to lose fat in a calorie surplus.
Due to this, bodybuilders prioritise one goal at a time.
They will spend a lot of time in a surplus, trying to build muscle while minimising fat gain.
Over time, they will eventually gain more body fat than they want. They then go into a calorie deficit.
Sometimes they do a longer cut. Other times they want it to be done quicker.
Unless you are very lean, often you can lose quite a bit of body fat relatively quickly without sacrificing much muscle.
Doing a 2–6-week aggressive cut can make sense for some bodybuilders or athletes.
The longer you spend in a deficit, the less time you get to spend in a surplus focused on muscle growth.
Typically, bodybuilders already have a great level of consistency and adherence to their nutrition. It puts them in a better position than most people for this type of approach.
Medical Situations Under Close Supervision
There are examples of VLCD approaches being used in situations such as type 2 diabetes with great success.
A study titled “The DIRECT Trial” involved just over 800kcal per day for 12-20 weeks.
One year from the start of the trial, 46% of participants had reversed their diabetes to the point of remission. At the two-year mark, 36% were still in remission.
These results are far better than what aiming for slow and steady weight loss does on average.
There are some other caveats though.
Following the VLCD they did a 2–8-week phase of reintroducing food in a systematic way. This approach is rare among people undertaking a VLCD by themselves.
Close supervision and support were also provided. It was a real-world study where participants were in control of what they ate. But there was a lot of support provided in the form of dietitian and doctor consultations.
Who Should Not Do Aggressive Diets?
Although I will have missed some scenarios, I would say that almost everybody not fitting into those guidelines should not do an aggressive diet.
Being more specific, people with a history of disordered eating should not do this approach. Even if the disordered eating was not recent, the risk is still quite high.
The other group I want to highlight is those who have tried aggressive diets more than once without success.
If you have tried something multiple times, and it has ended badly each time, it makes sense to explore different options.
A lot of people explore options by switching between different aggressive approaches. Instead, I would just be focusing on more moderate approaches.
Practical Summary
Aggressive diets should be used infrequently, and most people should not use them at all.
Keeping an open mind is important though. Some people can benefit from quicker weight loss than others.
If undertaking an aggressive diet, it makes sense to first identify if you are a good fit for that approach. Then it makes sense to ensure that you are in a good starting position to undertake one before you start it.
A final note I want to add is that it is helpful to have an end date for the diet as well as a plan to transition out of the approach. This aspect is often people’s undoing. Putting a plan in place could improve the odds of success and longer-term maintenance of the weight that is lost.
