Why does protein suppress your appetite?

  • The percentage of protein in your diet is highly correlated with how much food you consume. 
  • It’s not merely a matter of eating more protein, but rather, reducing energy from fat and non-fibre carbohydrates.  
  • We instinctively gravitate to foods that are highly processed.  These foods typically contain less protein and more carbs and fat.  
  • Minimally processed foods have fewer losses in processing due to dietary-induced thermogenesis.  Not only do we consume more calories from these foods but we also yield more energy to store as body fat.  

Background 

In our previous satiety analysis, we identified the dominant factors that influence hunger and satiety by analysing half a million days of MyFitnessPal data.

Now, using forty thousand days of detailed food diary data (i.e. both macronutrients and micronutrients) from more than a thousand Optimisers, we have validated our previous analysis and gained a deeper understanding of the degree to which the various factors drive us to eat more or less than we want to.  

The aim of this analysis of how people eat in the real world is to enable you to copy the behaviours of people who are successful and avoid common pitfalls of nutrition.  It has also allowed us to refine the Nutrient Optimiser algorithm to provide precise nutritional recommendations for Optimisers.

This is the first of an eight-part series.    

The word protein comes from the Greek word proteos, which means “of first importance.”  So it’s only fitting that we should devote this first article to protein.  

The data

The data analysed are from people trying to live their best life in the real world, subject to the stresses, temptations, beliefs, trends and fads, just like you.

While no dataset is perfectly accurate, forty thousand days of data from more than a thousand people enables us to deduce clear trends to identify the factors that have the most impact on our tendency to eat more or less than would like to.   

A wide range of dietary styles and preferences are represented (e.g. low carb, keto, plant-based, carnivore, paleo, etc.).  However, as shown in the table below, it seems Optimisers tend to consume more protein, fewer carbs and more fat than the typical modern western diet.  

We are often confidently wrong!

We often get lost in the minutiae of biochemistry and endocrinology trying to explain the mechanisms of what we believe will happen based on the action of hormones and peptides like insulin, glucagon, leptin, ghrelin, CLP-1, CKK & PYY etc.  

Unfortunately, this ‘understanding’ often leads us confidently down the wrong track.  Our limited understanding of biochemistry and endocrinology also don’t tell us much about what we should be eating for optimal health and satiety.

Our goal here is to empower you to make more informed decisions about food quality to reduce the burden of micromanaging food quantity and constantly fighting your appetite.  

The analysis

The basal metabolic rate (BMR) for each Optimiser was calculated using the Katch Mcardle Formula using their weight and body fat.   

The vertical axis on the satiety response curves below represents the user’s reported calorie intake for a particular day divided by their BMR.  

  • If the value is greater than 100%, we can assume they ate more than their BMR.  
  • If the value is less than 100%, it means they ate less than their BMR.

The data has been sorted and grouped into ‘bins’ of data for each parameter and the corresponding calorie intake/BMR calculated for each ‘bin’.  

Protein

The chart below shows % protein vs satiety response curve.   Optimisers who consume a higher percentage of protein tend to eat significantly less across the day. 

The impact of the percentage of protein on energy intake is massive!  People obtaining less of their energy from protein tend to eat 20% above their BMR, while people eating a higher proportion of energy from protein tend to eat up to 40% below their BMR!  That’s a range of more than 60%!

Spoiler alert:  This satiety response occurs when we consume foods with a higher percentage of calories from protein.  Unless you’re working out like Arnie, it’s not simply about eating more protein (which can come packaged with a significant amount of low satiety fat).  Sustainable weight loss is more about avoiding heavily processed, predigested energy from non-fibre carbohydrates and fat rather than necessarily consuming more protein.

What happens to ‘excess protein’?

You may have noticed in the chart above that the increase in satiety does not occur until we beyond 15 to 20% protein.  It appears that the initial intake of protein is “skimmed off the top” for muscle protein synthesis, growth and repair. Protein expert Professor Stuart Phillips likes to talk about protein as the building blocks of your body.

In a way, we can think of the protein used for muscle protein synthesis, the production of neurotransmitters etc as ‘free food’.  The first portion of your protein intake is not available to be used for energy, but rather is used as the building blocks to repair and maintain your essential bodily functions.  

For someone who is active or doing a lot of resistance training, this ‘tipping point’ may be significantly higher (say up to 30%), while it may be lower if you are sedentary (perhaps as little as 10%).

As we eat more protein above our minimum requirements, some of this ‘excess protein’ is converted to heat, some is excreted in the urine, and some is used for increased muscle protein synthesis and cellular repair.  

But, as your craving for protein is satisfied, your appetite for high protein food starts to decrease.  While you may find room for a doughnut or a cookie, you’re less likely to want to chow down more lean protein.  

Protein overfeeding studies consistently find that it is hard to gain weight when eating a lot of protein.  This appears to be partly because of the increased losses involved in converting protein to usable energy.  However, it’s also tough to get people to maintain a very high protein intake for a significant amount of time because of the powerful satiety response.  It’s possible that study participants are not able to meet their target protein intake (even when getting their protein from powders), and so they’re unlikely to be eating more than the allocated protein target because they feel so full!  

The observed satiety effect of protein aligns with the Protein Leverage Hypothesis, which suggests that:

  • we consume more food until we obtain the protein we need, and 
  • once we get enough protein, our appetite reduces.

Oxidative priority and thermic effect of food

The table below (adapted from Cronise et al., 2017) shows:

  • the order in which the different components of our food are used in your body (oxidative priority), 
  • what they are used for, 
  • their storage capacity, and 
  • the thermic effect of food.  

Because we have very negligible storage capacity for them in our bloodstream, alcohol and ketones are used for energy first, followed by ‘excess protein’, then by carbs and fat.  

It’s also possible that if you have plenty of fat and carbs available that your body will use those easier energy sources first and excrete some protein in the urine because it’s harder to convert to ATP.

Although carbs and protein can be converted to fat, it is usually the dietary fat that is stored because it is last in line to be burned.  Fat also requires less insulin to hold in storage, so it can easily be accessed, so long as we don’t have excessive amounts of other fuels lined up in front of it.

The thermic effect of food is the amount of energy that is lost to heat in converting that particular food to usable energy in your body (i.e. ATP).  Protein has a more complex chemical structure than carbs or fat, so it takes more energy for the body to break the carbon bonds to unlock the energy to be used in your body.  This thermic effect of food contributes to keeping you warm, but some people can even experience ‘meat sweats’ when they eat a lot of protein.

You’ll notice that the thermic effect of food value is shown as ranges.  A protein powder that is easy to digest may have a thermic effect of 20% while a piece of raw liver or kidney which is more complex may incur 35% losses in the conversion to usable energy.  

Similarly, there is a range for carbs. Acellular carbohydrates such as sugar or refined flour may be quickly and easily converted to ATP because they are effectively predigested, while an uncooked piece of broccoli or spinach will require more effort for your body to access the energy contained in that food.  

What about the official protein recommendations? 

Also shown on the protein-satiety response curve is:

It’s worth noting that the Estimated Average Requirement, Recommended Daily Intake and the population average all align with the lowest satiety response and maximum energy intake.   

How much protein do you need?

In addition to the percentage of energy you get from protein, your appetite works to ensure you get a minimum amount of protein.  As shown in the chart below (from Lemon, 1991), endurance athletes require a minimum of around 1.4 g/kg BW to maximise recovery, while a strength athlete will benefit from at least 1.8 g/kg BW.  If you’re not particularly active, you won’t need as much protein.  

What if you’re losing weight?

Because your body is only too willing to offload metabolically expensive muscle when food is hard to come by, you should target a higher protein intake when trying to lose weight.   

The chart below from a review paper by Stuart Phillips shows that the muscle preservation benefits are maximised at around 2.6 g/kg of body weight (BW) for someone who is in a significant deficit and doing resistance training.  

But it’s not just about eating more protein!

Because protein is strongly correlated with nutrient density and satiety, it’s better to err on the side of too much rather than too little.  But it’s not just about eating more protein.

As shown in the chart below, more protein correlates with a higher energy intake.  If your goal is to lose body fat, you need to ensure you don’t get too much low satiety energy-dense dietary fat along with your protein.

What’s a reasonable target for protein?  

To help you understand what is “normal”, we have analysed the protein intake in a number of ways.  

The protein distribution histogram chart below shows that the most common protein intake is 20-25%, with an average of 28%.  Few people manage to sustain a protein intake higher than 50%.    

The distribution chart below shows protein in terms of g/kg LBM.  The average protein intake of Optimisers is 2.0 g/kg LBM or 1.5g/kg body weight (BW).   

While we can’t equate percentage protein with g/kg of lean body mass (LBM) and g/kg of body weight (BW), we can see from the data that:

  • 25% of people are getting less than 20% of their energy from protein,  
  • 25% of people are eating less than 1.4 g/kg LBM, and 
  • 25% of people are eating less than 0.9 g/kg BW.

The table below shows the 25th percentile protein intake along with the average and 85th percentile for each of these ways of measuring protein intake.   

A calorie is not a calorie! 

Our good friend Ted Naiman (who makes these amazing infographics that he generously lets us use) likes to talk about the protein:energy ratio.   

We thought it would be interesting to dig into this concept a little further, to run the satiety analysis in terms of net energy (i.e. after muscle protein synthesis and losses due to dietary-induced thermogenesis), assuming:

  • protein up to 15% of your Basal Metabolic Rate will be used for muscle protein synthesis,
  • ‘excess protein’ not used in MPS yields 3.2 calories per gram (assuming a 20% thermic effect of food),
  • non-fibre carbohydrates yield 3.8 calories per gram (assuming a 5% thermic effect of food),
  • dietary fat yields 8.7 calories per gram (assuming 3% thermic effect of food), and 
  • fibre yields two calories per gram.

The chart below shows the relationship between energy intake and net energy (i.e. the energy available after muscle protein synthesis and losses due to dietary-induced thermogenesis).   

The next chart shows percentage protein and percentage available energy on the same chart. A reduction in the available energy from your food has a much stronger effect than even protein.  

Let’s unpack this a little more.  The table below shows the calories in each macronutrient if you burned the food in Bomb Calorimeter (i.e. one calorie raises the temperature of one millilitre of water by one-degree Celsius).   The dietary induced thermogenesis (DIT) is the amount of energy that is lost in the conversion of each macronutrient contained in food to energy to be used in your body (ATP) or storage as fat.  

macrocalories/gDIT assumedDIT rangeenergy yield (cal/g)
protein 420%20 to 35%3.20
carbs45%5 to 15%3.80
fat 93%3 to 15%8.73
fibre450%
2.00

As noted above, there is a range of dietary-induced thermogenesis for each macronutrient that would depend on the degree of processing (i.e. a raw food would require more energy to process in your body to use for ATP while a cook or highly processed food would require less).  If you wanted to maximise the thermic effect of food and minimise the calorie yield, you should prioritise minimally processed foods.

The first part of the protein you eat will not be available for use as energy (up to 15% of your BMR) but rather ‘lost’ to muscle protein synthesis to build and repair your body, create neurotransmitters and all the other important functions that protein does in your body.  The rest of the protein you eat can be used for energy if required, but some may be excreted, and a significant amount will be used converting that protein to usable energy in your body.  

Because this conversion process is so energy-intensive (with up to 35% losses) and because your appetite is optimised to obtain the maximum amount of energy with the least effort, your appetite will guide you to more efficient sources of energy such as highly processed carbs and fats.  Your appetite increases to make the most of any opportunity to get easy energy when it is available, especially if you are hungry and have not already filled up on nutrient-dense high satiety foods.

For better or worse, our modern food processing effectively pre-digests your food for you so you can get more energy with less effort. This ends up looking like carbohydrates and fats together in the same package in a way that rarely occurs in nature.  

A recent study by Kevin Hall showed that people tend to eat significantly more calories and gain weight if the food is heavily processed, even when matched for macronutrients and calories.  Not only do we tend to overeat foods that are heavily processed, but we are also able to obtain a lot more energy from them because of the reduced losses in converting that food into energy (i.e. lower thermic effect of food).  

So, once you have covered off your minimum amount of protein for muscle protein synthesis, if you want to reduce your overall energy intake without counting, weighing and measuring everything you eat, you need to focus on less efficient energy sources.  

This means you should focus on nutrient-dense minimally processed foods.  Foods and meals that contain more protein and fibre with less fat and non-fibre carbohydrates will be less efficient and provide more satiety.  Your appetite for these foods will switch off earlier, while foods and meals that contain more fat and carbs are less efficient and cause you to consume more energy.  

Some worked examples

To help you understand how this works in practice, let’s look at some examples.  

Optimiser average 

The table below shows the macro split of the average of the data from Optimisers.  In the first row, we have protein from which we ‘lose’ 15% for bodily functions, and have 80% of the remaining amount left for usable energy.  We lose 5% of the net carbs to dietary-induced thermogenesis and have 14% left. Similarly, for fat and fibre. In the end, we have 75% of the calories originally eaten to make ATP or to be stored as body fat after 25% of the calories consumed are used for muscle protein synthesis and lost in the conversion to energy.  

macro%DIT net energy
protein 28%20%7%
net carbs15%5%14%
fat 52%3%50%
fibre5%50%3%
total100% 75%

Population average 

In the next example, we have the population average macronutrient split.  In this scenario, all of the protein will be used for muscle protein synthesis with none left over to be converted to energy.  In the end, we have 84% of the calories consumed available for energy or to be stored as fat (i.e. compared to the Optimiser average, 9% more of the energy ingested is available for conversion to ATP or storage as body fat).

macro%DIT net energy
protein 12%20%0%
net carbs44%5%42%
fat 42%3%41%
fibre2%50%1%
total100% 84%

The most nutrient-dense foods

In this last example, we have the most nutrient-dense foods, which not only contain a lot of nutrients, but also a significant amount of protein and fibre which tend to be present when we prioritise foods that contain more of the harder to find vitamins, minerals and essential fatty acids. 

Although the dietary-induced thermogenesis for each macronutrient would likely be much higher because the nutrient-dense foods are typically less processed, we have used the same DIT values. 

In this scenario, we end up with more leftover energy from the ‘excess protein’, but a lot less available energy from fat and non-fibre carbs. So the available net energy is calculated to be 66%.  The net energy value aligns with the lowest value we see in the data from Optimisers.  

macro%DIT net energy
protein 42%20%19%
net carbs17%5%16%
fat 23%3%22%
fibre18%50%9%
total100% 66%

Comparison 

For comparison, the chart below shows the Optimiser average and the population average along with the net energy available from the foods that have the highest nutrient density.   Not only would you be consuming around 60% fewer calories by prioritising nutrient-dense minimally processed food, but you will also absorb a lot less of those calories while still obtaining the micronutrients you need to thrive!  

To make this a little more relatable, the table below shows the macronutrients and the calculated net energy for a number of popular dietary approaches.  The macronutrient profile is based on our nutrient-dense food lists for various goals, so they are the best versions of each of these approaches.  

approach
protein net carbsfat fibrenet energy
population average12%44%42%2%84%
carnivore36%3%61%0%76%
keto20%2%71%7%75%
low carb30%8%47%15%70%
plant-based22%40%10%28%64%
max nutrient density42%17%23%18%66%

The net energy for each approach is shown in the chart below.  Because they all tend to move you away from processed food that tends to contain more protein and fibre, we end up with diets that yield a lot less net energy (i.e. after muscle protein synthesis and dietary-induced thermogenesis).    

One caveat here is that, while a nutrient-dense plant-based diet will be tough to overconsume due to its very low energy density, it is still lacking several essential micronutrients, particularly vitamin B12 and omega 3 (as shown in the comparison of the nutrient fingerprint charts below).  Also, in the real world, people tend to gravitate to a ‘plant-based’ diet that relies heavily on oils and refined grains so they may not get the full satiety benefits.  

What about carbohydrates and insulin?

Because we have data on the short term (bolus) insulin response to food, many people are concerned about the insulin response that we see with protein and carbohydrates, and treat fat as a ‘free food’ because it does not appear to raise insulin as much.  But it’s more important to focus on your total insulin levels across the day, not just after meals.  

Your insulin requirements across the day are related to how much energy you need to hold in storage while you use up the energy from the food you are eating.  If you focus on high satiety foods that allow your body fat stores to be used for energy, your total insulin requirements across the day will plummet to enable your body fat to be used for energy.  

It’s not:

Carbs -> insulin ->  fat storage 

But rather:

Low satiety nutrient-poor foods -> increased craving and appetite -> increased food intake -> fat storage -> increased insulin

If you are looking to lose body fat, your highest priority should be to reduce hyper-palatable nutrient-poor processed foods.  

If your blood sugars are still elevated after meals (i.e. above 140 mg/dL or 6.8 mmol/L), then you should look to reduce your carbohydrate intake until they stabilise.  

How to implement a high satiety diet  

One ‘problem’ with higher protein intake is that abrupt changes can force a significant and uncomfortable energy deficit which, in spite of increased satiety on a calorie for calorie basis, is still not going to be easy!  If you were looking to lose body fat, the ideal approach would be to increase your percentage protein slowly and continue to refine your diet until you get the results you want.  

You can think of Dietary Induced Thermogenesis as resistance training for your metabolism. If you’re not getting the results you want then you may benefit from a little more.

Rather than just prioritising protein, it’s ideal to prioritise high satiety nutrient-dense foods and avoid foods that are a combination of fat and carbohydrates together.  The foods to avoid are typically highly processed foods that require flavours and colourings to make up for their lack of taste and nutrition in highly refined ingredients.

Where do I start?

After four years of digging into the theory, we’ve created some exciting tools to help you implement the theory:

Keep reading

In our next article in this series, we will look at the satiety response to carbohydrates, fat, sugar, alcohol.

To kickstart your journey towards optimal get your free program and one of 70+ food lists personalised just for you!  

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