Fat loss is some that from a nutritional perspective is somehow both simple and incredibly complex.
Understanding nutritional priorities when it comes to fat loss can make the process seem simple. It can also make it easy to avoid focusing on things that do not really matter.
But it can be ridiculously complex when you factor in all the details that can be relevant.
This post is going to cover the fundamentals of nutrition for fat loss, while also touching on a lot of practical points.
As a dietitian writing about nutrition for fat loss, the training/exercise aspect will not be discussed in this post. But if your goal is fat loss, it makes sense to also be training or exercising in an effective manner that also lines up with your goals.
Calories in vs Calories Out
The overarching fundamental principle involved in weight management is calories in vs calories out (CICO). This should not be a controversial statement.
Our body is literally made up of calories. Our muscles and fat are stores of calories, even though they might also have other functions.
The body burns through calories every day doing a variety of things.
For example, your heart pumping, lungs breathing, brain functioning, literally maintaining the amount of muscle and fat you have, in addition to a massively long list of things, burns calories. This is before even factoring in the calories burned during movement.
When there is a surplus of calories, beyond what the body has burned, that surplus gets stored in some way. Fat is one of the options for where it can be stored.
When there is a deficit of calories, as in the body has burned more calories than what has been consumed through food, these calories have to come from somewhere.
Like literally think about that, if the body has burned X number of calories, but you have eaten less than that amount, where do the calories come from? Our body’s main storage form is muscle and fat, so it comes from there.
This overly simplified explanation is why CICO works. Breaking it down to this level is important because it also prevents other misunderstandings.
There is obviously more to the story. The “calories out” portion of the equation is not some static number that stays the same day in and day out. There is a lot of variation in that number. Heck, even the number of calories you eat directly changes that number.
This image below from Alex Thomas (President of Sports Nutrition Association) highlights how although creating a calorie deficit for fat loss can sound simple, there are a lot of factors going on that determine the calories out portion of the equation.
How to Figure Out How Many Calories You Need?
As mentioned above, you need a calorie deficit. The starting point should be to roughly figure out what your maintenance calories are.
You can do that by using this calorie calculator. Do not rely on the number any calculator or formula gives you though. It is just an ESTIMATE.
If there is no rush, the first step could be to try and find your maintenance calories. You could eat a certain number of calories for a couple of weeks.
If you maintain your weight, those are your maintenance calories. If you lose weight, that was a deficit. If you gain weight, it was a surplus.
Alternatively, I prefer to have people jump straight to a deficit, so that they most likely see progress right off the bat.
A solid starting point for most people is to take 20% away from their maintenance calories. This should result in weight-loss at a moderate pace. But just adjusting that as needed.
A calorie deficit results in weight-loss if followed consistently for a sufficient period. So, if your weight is not decreasing, you are not in a deficit.
There are also some caveats I want to add:
- You do not NEED to track calories. Calories matter whether you track them or not. I have written this as if you were going to have an accurate gauge of however many calories you have. But the principle is still that you need an appropriate number of calories for your goal.
- You do not NEED a deficit to lose fat. It is possible to recomp. You can maintain your weight and lose fat. Fat loss is typically less efficient than a deficit, but it can happen. It also often requires the odds to be stacked in your favour in terms of some of the following factors: Sufficient protein intake, good sleep, good training, good genetics and not already being at an advanced stage with your training.
Can You Go Too Low Calorie?
A lot of people refer to a concept of “going so low calorie that your body goes into survival mode that it holds onto fat” as a reason why you should not go low calorie.
That comes from a small bit of truth, which I will talk about later. But typically, the concept is taken too far.
“Starvation mode” is not a thing. To put it clearly, the lower calorie you go, the more fat you lose.
Think back to the fundamental principles. If you have minimal calories coming in, but you are burning a certain number of calories, where do they come from? They come from your body’s stores e.g. muscle and fat.
Going excessively low calorie does not prevent fat loss. The deficit must be accounted for in some way.
That being said, the body can take steps to conserve energy and reduce energy expenditure. This decreases the calories out portion of the equation.
This concept is known as metabolic adaption, which will be discussed later.
It is important to understand that while calorie expenditure can drop due to this, it often is not by an extreme amount. And it typically does not exceed the change in calories.
Reducing calorie intake by 500kcal typically does not lead to a metabolic adaption reducing energy expenditure by >500kcal. A much smaller reduction is expected.
Does that mean that going excessively low calorie is a good idea? Not in the slightest. It just means it does not prevent weight loss.
Going excessively low calorie can increase risk of muscle loss, increase fatigue, increase irritability, make it more difficult to adhere to the plan, reduce immunity, make it harder to reach micronutrient targets and a whole lot of other issues.
Part of the reason why this issue has been discussed though is due to underreporting. Not many people talk about this, but on average, people significantly underreport what they eat, and overreport how much they exercise.
In this study, participants who were self-identified as diet resistant, were monitored for a period of time and then did a recall of what they ate during the process.
On average, what they said came out as 47% less calories than what they did. Nobody was within 20% of the calories that they had. Everybody underreported by a minimum of 20%. And somebody underreported by as much as 80%.
In terms of exercise, on average they overreported by 50%.
That 20% number is the most interesting to me. Since it means that we probably should assume that everybody in this situation underreports by at least 20%.
This does not make people liars. It is just pointing out that humans struggle to communicate what they do and may also struggle with recall.
For most situations that do not seem to make sense because somebody is not losing weight while on what would be expected to be a large calorie deficit, it is worth considering this possibility before jumping to alternate conclusions.
Calories control what we weigh. But other aspects influence our body composition in different ways. Protein is one of those aspects.
If your goal is fat loss, this is slightly separate from a goal of “weight loss.”
For example, a calorie deficit could dictate that you lose 5kg over a certain timeframe.
If you followed a low protein diet of the course of that 5kg loss, you would likely lose a significant amount of muscle.
If you had more protein, within your calories, you would likely lose less muscle.
If you lose the same amount of weight, but maintain more muscle, you have therefore lost more fat.
Protein should be prioritised while looking to lose fat, for this reason.
In terms of the amount of protein, my standard recommendation for a lot of clients is 1.6-2.2g/kg of body weight per day.
If you are quite lean already, it makes sense to go higher. If you have a lot of body fat, it makes sense to go a little bit lower, like 1.4g/kg of body weight.
This is because the range is mostly based on how much muscle you have.
If you want a number based on fat-free mass, my recommendation would be 2.3-3.1g/kg of fat-free mass, per day.
You CAN still lose fat on a lower amount. I would just recommend going as high as this if you are either looking to preserve as much muscle as possible throughout the process, or gain muscle throughout the process.
You can also go higher than these numbers if you want. There are minimal downsides from going higher (assuming no medical conditions preventing this, for example this is assuming that kidneys are health), beyond that it takes away from the opportunity to consume more carbs and/or fats, in addition to the benefits associated with those.
Carbs vs Fat Debate
There has long been a debate between whether low carb or low fat is more effective for fat loss.
The low carb aspect is often argued based on thinking around how insulin impacts fat loss/gain, as well as discussions around satiety and desire to eat.
A main argument for low fat is that when you look at the calories per gram, it can make logical sense to see fat as an easy way to reduce calories.
Carbs have 4kcal/g
Protein has 4kcal/g
Fat has 9kcal/g
Fat has more than 2x as many calories per gram than protein and carbs.
Without going too far down this rabbit-hole, the answer is that both options work.
In a controlled environment, when calories and protein are matched, over an extended timeframe, both options result in similar fat loss, although very slightly leaning in favour of the low fat approach.
From my perspective, the difference is irrelevant.
It is worth being aware that lower carbohydrate intake typically leads to a reduction in glycogen weight and water weight. This can lead to quicker weight loss in the first 1-2 weeks, but this is not representative of what is happening from a fat loss perspective.
Moving on to another argument: What happens in a real-world situation?
People can make compelling arguments in terms of which approach is easier to stick to for most people.
But when studied on a large scale, in a real-world environment where people are looking after their own nutrition, the results still come out similarly on average.
While this leads to a lot of confusion for people, I think it actually simplifies it. Both options work similarly. Instead of focusing on carbs vs fat, it makes more sense to focus on calories and protein.
And then just focusing on an approach that allows you to achieve that consistently, while still achieving an overall quality diet.
Why Fat Burning Is Not the Same as Fat Loss
One of the things this fundamental understanding of nutrition for fat loss is useful for, is determining what is and is not worth paying attention to.
A lot of products and strategies are referred to as helping with fat loss.
But a fundamental understanding of how calories work can help identify why “fat burning” (also known as fat oxidation) can be relevant but should not be overhyped.
Let me use an example to explain:
Two people eat 2000kcal per day. And let’s say this is their maintenance calories.
They both do 400kcal worth of cardio.
But one does it fasted. The other one does it after eating breakfast.
Technically, the one who does it fasted burns more fat during the cardio session.
But does this translate to greater fat loss over the course of days/weeks/months? Nope.
The reason for this is because total calories are matched. They both burn the same number of calories across the day.
One burns more fat in the session because they have less carbs/glucose/glycogen available. The other burns more glucose in the session.
But over the course of the day, this balances out. At other stages of the day, the fasted cardio individual has more carbs available to burn, since they had more carbs later in the day.
The fed cardio individual had less carbs available later in the day so burned more fat.
A similar example is how increased dietary fat intake literally means you burn more fat. Because you have more fat available.
Some people will say “this turns your body into a fat burning machine” which sounds great. But there is still more dietary fat to burn through before you reach your body’s stored fat.
Fat burning is referring to the acute timeframe. Fat loss is in reference to the total amount that of fat that is lost over a longer timeframe. Fat loss is what we care about, not necessarily how much fat is burned.
The “It’s Not Calories, It’s Hormones” Debate
A lot of people who argue against CICO make the argument that it ignores hormones.
But it does not actually do that. Hormones and calories are intertwined.
Hormones can impact the calories in part of the equation. They can increase appetite and desire to eat. One example is how increased ghrelin can drive appetite.
They can also influence the storage of calories. For example, higher testosterone can make it more likely that calories are stored as muscle instead of fat.
There is also an impact on the calories out portion of the equation. A decrease in T3 (triiodothyronine) can result in a reduced energy expenditure.
Being in a deficit for an extended period of time changes hormone levels. Being in surplus changes hormone levels. They go hand in hand.
Focusing on calories does not mean you should ignore hormones. Focusing on hormones does not mean you should ignore calories.
They are separate concepts, but they influence each other. Both are important. It is not just about one vs the other.
A lot of this post has been theoretical, so I wanted to discuss some practical strategies that help.
Firstly, appetite is a huge factor that can make it difficult to create a deficit.
Most people typically reduce their portion sizes in a bid to reduce calories. This approach does create a calorie deficit, but in my opinion, it can also make sense to manipulate calorie density of foods as well.
This is a concept called “volume eating.” By eating a higher volume of lower calorie foods, you can eat more food, while reducing your calorie intake.
It allows you to feel fuller and more satisfied while getting leaner.
One example of this is vegetables. Very few people think of vegetables as filling. But PER CALORIE, they are incredibly filling. Increasing vegetable intake can help manage appetite.
On that topic, increase fibre intake also helps with appetite. A general guideline is 25g of fibre for women and 30g for men, but I think it is worth playing around with this and figuring out what works best for you. There can be a lot of arguments that can be made for going higher than this.
Protein is also the most satiating macronutrient per calorie, so this is another reason to focus on protein as well.
It is also worth choosing a deficit size that is appropriate for you.
Theoretically, a 500kcal deficit results in roughly 1/2kg per week weight loss, assuming it all comes from fat. Double the deficit for double the rate of fat loss.
It is NOT that simple though. As mentioned earlier, changing your intake changes your expenditure. And this changes more in some than in others.
But this is a good guideline. If you want to lose faster or slower, you adjust the size of the deficit.
It makes sense to choose a deficit that fits your lifestyle and goals best. Going too aggressive can have downsides that have been mentioned above. But going too slow could draw the process out excessively long too.
And the last practical aspect I wanted to mention is that taking a flexible approach can make this process easier.
Making the plan excessively strict can make it more difficult than necessary and might reduce the likelihood of success.
It is also worth being aware that being more flexible also likely does not negatively impact your results. There is a reason why IIFYM (If It Fits Your Macros) has gained so much popularity.
Having a little bit of sugar also is not detrimental from a body composition perspective. If it is within your calories and macros it does not prevent fat loss noticeably.
One study even compared 10g sugar per day to 100g sugar per day, in the context of the same calories and macros, to show that this difference does not matter. This is a pretty big difference in total sugar and there was no meaningful difference in results.
A lot of people have gone on to test this and come to the same conclusion. There is no point stressing about a small amount of sugar in food, particularly if that flexibility makes it much easier to stick to the plan.
Why Do Plateaus Occur?
If you have a lot of weight to lose and you start off with a small/moderate deficit, and do not adjust calories throughout the process, you are guaranteed to run into a plateau. This is because literally losing muscle/fat reduces your calorie expenditure.
Heck, use that calorie calculator as an example. Put in your details at X body weight. Then put in your details at X minus 10kg body weight. The new calorie target will be lower.
Losing weight literally reduces calorie expenditure.
But plateaus are more complex than that.
Before talking about the behavioural side of things, it is worth discussing metabolic adaptation.
Being in a deficit for an extended period of time means your body starts trying to reduce calorie expenditure. The larger the deficit, the more severe this response typically is.
This can be done by reducing heart rate, reducing core temperature, downregulating certain process.
It also explains why a lot of women lose their period when they are either in an extended deficit or they get particularly lean. The body tries to shut down or reduce all non-essential uses of energy.
If there are not enough calories coming in, a non-urgent process like reproduction no longer seems like as much of a priority.
The most interesting aspect for me though is that incidental movement seems to drop off as well.
This can be stuff like an unintentional drop in daily steps. A reduction in fidgeting. A reduced desire to do small chores around the house. Little things like that.
All these factors burn calories, so energy expenditure drops when these factors are reduced.
This can contribute to plateaus.
It is also worth mentioning that habits change. Maybe the novelty of dieting has worn off. Maybe somebody is not sticking as closely to their plan as they were at the start. Maybe they are exercising less, or less intensely.
There is a pretty long list of factors.
It is also worth being aware that hunger and desire to eat typically increase over the course of a diet.
For example, in the image below, the group that dieted for 12 weeks straight clearly increased their appetite. And the desire to eat chart (not pictured) looks quite similar.
Over the course of a diet, somebody can start to develop a larger appetite and drive to eat. This is part of the body’s response to a reduction in calories. It also partly explains why people often regain weight.
Plateaus occur due to a combination of the factors above, as well as countless other factors.
To get past a plateau, the main options are:
- Reduce calories further. Either through more consistency (if not already consistent), or through a planned reduction in calories.
- Increase energy expenditure.
- Take a break from the deficit and set yourself up for the future. This could involve a “diet break” which is a period of time at maintenance calories. If done for long enough, this could reverse some of the metabolic adaptation that has occurred, while also reversing the increase in hunger and psychological aspects of dieting.
Tips for Maintaining Fat Loss
Statistically speaking, a large percentage of people who lose weight, regain weight.
Based on the research, my interpretation is that around 80% of people who lose weight, regain weight within a year. And the data looks worse the longer the timeframe gets.
It is a minefield when you try to get clear statistics on this though. Because what is defined as weight regain? How do we account for people who drop out of studies? There are a lot of factors to consider. But basically, we can all agree that a large percentage of people regain weight.
So how do we improve the odds of maintaining fat loss long term?
A few strategies I see are:
- Sufficiently high protein intake: Keeping protein intake higher has advantages in terms of higher amounts of muscle mass (which also translates to slightly higher resting metabolic rate), slightly more calories burned through the thermic effect of food and slightly more satiation per calorie.
- Utilising diet breaks during the fat loss phase. This allows the opportunity to practice time spent at maintenance calories. Not everybody needs to do this, but it could be helpful for a lot of people.
- Continuing to exercise at a decent duration and intensity. People who continue exercising at a similar amount to what they did during the fat loss phase are significantly more likely to maintain that fat loss.
- Build good habits in terms of maintaining fibre intake and ideally having a good amount of fruits and vegetables.
- Getting good sleep. This literally improves body composition, but it also can reduce hunger and cravings. Insufficient sleep also means more hours awake and increases likelihood of consuming more calories due to this.
- Have a “relapse plan” in place for if body fat increases beyond a normal fluctuation. This could mean going back to what was effective for dropping fat in the first place.
- Maintain a flexible approach. Dichotomous thinking is strongly associated with weight regain.
If I went through every tip I could think of, this list would be exceptionally long. But literally just implementing the above, dramatically stacks the odds in your favour in terms of maintaining that fat loss.
A lot of people focus on the wrong things when it comes to fat loss. When you get into the details, it can become a complex topic.
My main piece of advice is to focus on the big details that matter most (such as calories and protein) and then look at other areas in order of priorities.
The best advice I can give is to avoid missing the forest for the trees. If you find a small detail interesting, the first test is to see if it takes you away from what you want to be doing with the big details. If the answer is no, it could be worth implementing. If the answer is yes, it might be worth focusing on the big picture, because that is what is going to lead to the outcome you are looking for.
Aidan is a Brisbane based dietitian who prides himself on staying up-to-date with evidence-based approaches to dietetic intervention. He has long been fascinated by all things nutrition, particularly the effects of different dietary approaches on body composition and sports performance. Due to this passion, he has built up an extensive knowledge base and experience in multiple areas of nutrition and is able to help clients with a variety of conditions. One of Aidan’s main strengths is his ability to adapt plans based on the client’s desires. By having such a thorough understanding of optimal nutrition for different situations he is able to develop detailed meal plans and guidance for clients that can contribute to improving the clients overall quality of life and performance. He offers services both in-person and online.