Protein and Weight Loss - The Ultimate Guide

Woman and man showing abs

Protein is the most important macronutrient for weight loss: it's more satiating than carbs and fat, you burn more calories digesting it and it helps you retain your muscle mass while you lose body fat.

Have a read of the full guide to find out more about how much protein you need, where you can get it from and when you should eat it.

You’ll also find out about why it’s not really bad for your kidneys and which sources of protein to eat to minimise your carbon footprint.

1. What is protein and what’s it for?

Illustration of numbers standing on a podium

Proteins provide your body with the structural integrity that prevents you from being nothing more than a motionless pile of goo on the floor.

Amino acids are the building blocks of protein. Nine of these are essential which means you can’t manufacture them yourself. You have to get them from your diet.

The amino acids in your diet contribute to making the following structures:

  1. Fibrous proteins such as collagen, elastin and keratin (found in bone, teeth, skin, tendons, cartilage, blood vessels, hair and nails)
  2. Skeletal muscle (the muscles you contract voluntarily to move yourself around)
  3. Smooth muscle (the muscles you contract involuntarily, including blood vessels, lungs, gastrointestinal tract)

In addition to making up the more obvious physical architecture of your body, proteins are also involved in a number of essential processes that go on under the hood.

Enzymes involved in the breakdown of fat, hormones (including glucagon and leptin) which help regulate fat storage, and neurotransmitters that aid communication between your brain and your muscles are all made from protein.

While enzymes and hormones are undoubtedly important, it's your skeletal muscle mass which is impacted the most by the dietary protein you consume, especially if you do strength training.

You can’t just store protein for later in the same way you can store fat so you must consume it in sufficient quantities, regularly, if your goal is to gain muscle mass.

But, what if you don’t care about increasing muscle mass and just want to lose weight? Well, unless you want to be a 'skinny fat' version of your current self, you’ll need to hold on to as much muscle as possible while you lose weight. This is where higher protein diets can help with healthy weight loss (especially when combined with strength training).

Key Takeaways

  1. If you want to achieve optimal health and performance you must consume enough essential amino acids in your diet.
  2. Even if you have no interest in bulking up, a higher protein diet will help you maintain the muscle you already have while you lose weight.

2. Protein Mythology

Illustration of a 3 headed chicken

Let’s get this one out of the way first because it’s the most commonly held objection to a high protein diet:

'What about my kidneys? Won’t they implode if I eat too much chicken?'

No. Not too much chicken, eggs, beef, salmon, soy burgers or even protein shakes.

According to Stuart Phillips, PhD, one of the world’s leading experts on protein, there is zero data linking protein intake to the development of kidney disease.

The myth that protein is bad for your kidneys has its origins in some faulty, circular logic originating in the renal wards of hospitals (where trainee dieticians spend some part of their training).

Patients with chronic kidney disease (CKD) and renal failure are put on a low protein diet which has been shown to prolong their survival. So, less protein = longer life, right?

If you have CKD, then the answer is yes. If you don’t, then the answer is no. The faulty logic is concluding that protein causes renal failure in everybody. It doesn’t. It just makes things worse when your kidneys are already damaged.

However, in the current media climate where fear-inducing headlines get more clicks than nuanced science, the boring facts often get lost amongst the noise. Incidentally, after the media’s demonisation of fat, carbohydrates and protein, the only remaining macronutrient as a possible source of calories is alcohol.

In this presentation, Phillips explains that the measure of kidney function is glomerular filtration rate (GFR). To back up his claim that there is no evidence to show that GFR and kidney function are adversely affected by a high protein diet, he quotes the most recent Dietary Reference Intake (DRI) guidelines.

These are put together by the Institute of Medicine (IOM), and their conclusion reads: ‘protein content of diet is not related to progressive decline in kidney function with age’.

Protein doesn’t damage your kidneys. Even if you eat a lot of it. It just speeds up your death if you already have CKD.

The next biggest myth regarding protein is that consuming too much of it makes your bones weak. The theory went that protein increases the acidity of the blood which, in turn, causes leeching of calcium (which is alkaline) from the bones in a homeostatic effort to reset the blood’s correct pH. However, as Phillips explains in the same video, there is no evidence to support this claim either.

In fact, there is substantial evidence to support the contrary claim that a higher protein diet is associated with stronger bones. This may be because protein stimulates the growth (or at least the retention) of muscle tissue which makes you stronger. This in turn allows more force to be applied to your bones, thereby making them stronger. This is why resistance training is recommended to prevent osteoporosis in peri-menopausal women.

Key Takeaways

  1. Protein doesn’t damage your kidneys unless you already have CKD.
  2. And it doesn’t make your bones weaker (it will in fact help make them stronger if you also do resistance training).

3. Why protein is king for fat loss

Illustration of a roast chicken wearing a crown

Let’s first make it clear that weight loss is only possible when you’re in a caloric deficit, i.e. when you consume less calories than you expend. This is non-controversial, despite much nonsense to the contrary spouted on social media by the nutritional equivalent of flat-earthers.

Claims are often made that fat gain is all down to hormones (particularly insulin) and that calories are unimportant (hence the popularity of low carb fad diets). While insulin may be involved in storing body fat, this can only happen while you’re in a caloric surplus, i.e. you’re eating more calories than you need. The demonisation of insulin has been thoroughly debunked here.

So, in practice you will lose weight irrespective of the proportion of fats, carbohydrates and protein in your diet, as long as you’re in a caloric deficit.

However, protein has intrinsic characteristics that make it easier for you to maintain the calorie deficit required to lose weight.

(1) Protein increases satiety

It’s not just the quantity of food that makes you feel sated. The quality of what you eat can also have a profound effect on your level of hunger.

Whereas processed carbohydrates like white bread and cookies are known to induce cravings for more of the same, protein has been shown to be the macronutrient that reduces hunger most effectively. When it reaches your stomach it raises the level of peptides which in turn send satiety signals to the brain making you less hungry and less likely to overeat.

An example of protein’s satiating effect is a study by Weigle et al showing that in ad libitum conditions (where subjects are free to eat as much as they choose), increasing protein intake from 15% to 30% of total energy resulted in a spontaneous drop in energy intake by 441 kcal/day. This led to a body weight decrease of 4.9 kg in 12 weeks.

In other words, if you’re consuming less than optimal amounts of protein, then add some more to your diet to replace some of the carbs and fat. Your appetite will likely decrease slightly as a result and make it easier for you to achieve the calorie deficit required for fat loss.

(2) Protein has a higher thermic effect than the other macronutrients

On average, about 10% of all the food you eat will be burned up through digestion. This is known as the thermic effect of food (TEF). However, the precise amount of calories you burn digesting food depends on what type of food you eat. The three main macronutrients have different TEFs:

Fat has a TEF of 2-3%

Carbohydrate has a TEF of 6-8%

Protein has a TEF of 25%

So, 25% of the calories you get from protein are used just to digest it. This means that if you replace some of the carbs and fat in your diet with protein, it should be easier to lose weight even if you eat the same amount of food.

*It should also be noted that mixed meals (a combination of carbs, fat and protein) have a similar TEF to eating protein in isolation so you don’t need to eat exclusively protein to get this benefit. Just make sure to include some protein with every meal.

(3) Protein helps you preserve your muscle mass while you lose weight

When you lose weight you usually lose some muscle as well as fat. If you’re sedentary you can expect around 30% of the total weight you lose to be muscle. This is how some people end up looking 'skinny fat’ instead of ’toned' after going on a diet without exercising.

However, if you practice resistance training while you're in a calorie deficit you can expect to hold on to a higher percentage of your muscle so that a greater proportion of the weight you lose is fat.

To maximise results you need to make sure you’re consuming adequate protein to fuel the increased rate of protein turnover (the breakdown and regeneration of muscle tissue) caused by the resistance training.

If you train hard enough and follow the right diet it’s actually possible to lose body fat and gain muscle at the same time, as demonstrated by the following tightly controlled study from The American Journal of Clinical Nutrition:

Two groups of young male athletes took part in an intensive training program (6 days per week) for 4 weeks, while in a 40% calorie deficit. Both groups consumed the same number of calories, however, one group consumed a high protein diet (2.4g/kg bodyweight), and the other group consumed a moderate protein diet (1.2g/kg bodyweight).

Both groups lost weight. Both groups lost body fat. Neither group lost muscle mass.

However, the notable difference between the groups was that the higher protein group actually gained muscle at the same time as losing weight and losing body fat. They also lost slightly more fat than the control group.

It's also fair to assume that they probably hated the experience – hard training 6x per week while in a 40% calorie deficit isn’t realistically sustainable.

Key Takeaways

  1. Sensible choices beat will power. If you include more protein in your diet you will be less hungry, and therefore more able to eat less and lose weight as a result.
  2. Eating protein with every meal increases the amount of calories you burn through digestion alone.
  3. Protein helps you preserve your muscle mass (and can even help you increase it, albeit under extremely challenging conditions) at the same time as you lose weight and lose body fat while in a calorie deficit.

4. How much protein do you need?

Illustration of fish and eggs on a weighing scale

If you’re thinking that 2.4 g of protein per kilo of your bodyweight is more than you would ever be able to eat consistently, then you’re probably right.

And you most likely don’t need to unless you’re a steroid user, a genetic freak (with an unusually high capacity to build muscle) or a vegan (proteins from plants are usually inferior to proteins from animals in terms of both bioavailability and amino acid profile so, vegans are advised to increase their protein intake beyond the requirements of an omnivorous diet by around 20%).

The exact amount you need depends on many factors including your weight, your goal, your activity levels, your training experience and your age.

As a baseline, let’s start with healthy, sedentary adults. The recommended daily allowance (RDA) in the US is 0.8 g/kg bodyweight/day. However, it should be noted that this number represents the minimum amount required to prevent malnutrition. So, it’s hardly an ideal target to aim for.

More modern methods at determining protein requirements have suggested that around 1.2g/kg/day is a more appropriate minimum RDA for healthy young men, older men, and older women.

That’s if you spend all day sitting down.

If you exercise, thereby increasing the rate of protein turnover in your muscles, you'll need to eat more protein than the RDA.

And if you strength train, which is advisable if you want to hold on to your lean mass (muscle) while you lose weight, then you’ll need a bit more.

As Alan Aragon explains in The Lean Muscle Diet, a strength trainee who wants to be leaner is putting demands on his or her body that require more protein:

'Now you’re deliberately increasing the rate of muscle-protein breakdown, with the goal of creating new muscle tissue at an even higher rate. Logically, that requires more protein from your diet. Now add another element: a lower-calorie diet. The diet puts stress on your muscle tissue in two ways. First, it gives your body less overall energy to support the process of muscle repair and growth. Second, that protein in your muscles can become a source of energy when you’re eating below maintenance levels. The leaner you are, the smaller your margin for error before your body turns to muscle tissue for fuel.'

So, how much protein do you need exactly?

  • Sedentary adults: 1.2-1.8 g/kg
  • Adults wanting to gain muscle: 1.6-2.4 g/kg
  • Overweight/obese adults wanting to lose body fat: 1.2-1.5 g/kg
  • Pregnant women: 1.7-1.8 g/kg
  • Lactating women: at least 1.5 g/kg
  • Older adults (over 65): 1.2-1.8 g/kg
  • Older adults (over 65) who want to lose body fat: 1.5-2.2 g/kg
  • Older adults (over 65) who want to gain muscle: 1.7-2.0 g/kg

Experienced trainees who are already lean may benefit from exceeding the upper end of these recommendations, going up to 3.3 g/kg. However, this won’t help them gain more muscle.

It will only help them minimise the fat they store while they gain the muscle. Respected researcher, Menno Henselmans points to studies which show that most people get no additional benefit from eating more than 1.6 g/kg. He suggests targeting 1.8g/kg/day (0.82g/lb/day) in order to have a buffer.

In my experience, if you want optimal results, this is a realistic target to aim for. Most people will struggle to eat more than this anyway.

Going by this recommendation, a 60kg female should aim for around 108g of protein per day.

And a 90kg male should aim for around 162g of protein per day.

If that still sounds like a lot, and you have no idea how much protein your meals contain, you can start off by aiming for 1-2 palm-sized portions of protein-containing foods (listed below) with every meal.

Key Takeaway

  1. The RDA for protein is insufficient for optimal health. Sedentary adults can get away with eating 1.2 g/kg to meet their daily requirements. Adults who engage in strength training and who want to either gain muscle or lose body fat should aim for around 1.8 g/kg/day.

5. When should you eat protein?

Illustration of protein-containing foods on a clock in place of numbers

Most research suggests that the number of meals you have per day doesn’t affect how much total energy you expend, how much muscle you build or how much fat you burn. Dividing your food up into 6 meals per day in order to 'rev up your metabolism’ has now been confirmed to be just another myth.

For most people, 3-5 meals per day is more realistic (where snacks count as meals).

How often you eat should be down to your personal preferences and lifestyle. However, there are some considerations depending on what time of day you train, how much training experience you have and how old you are.

(1) Do you need to down a protein shake instantly after your workout?

There's an 'anabolic window' after you train in which training-related muscular adaptations occur. If you’re just starting strength training this window lasts about 72 hours. So, there’s no actual need to go rushing to the locker room and fumbling for your protein shaker before you get in the shower.

Your body is in a constant state of regeneration due to the large amount of muscle remodelling that needs to take place. So, as long as you’re getting 3 or 4 meals a day with at least 0.4 g/kg protein per meal, the timing of those meals in relation to your training sessions isn’t important.

However, the more training experience you have, the more your anabolic window shrinks until it gets down to about 24 hours. So, an advanced trainee who trains 3 mornings per week should consume a higher proportion of their weekly protein on those days.

If they train 3 evenings per week, then it would be advisable to consume the bulk of their weekly protein on the evenings they train and the following mornings.

Experienced trainees who have a higher training frequency, for example 6 days per week can divide their protein requirements more evenly throughout the week, in the same way that novices can..

(2) Is it better to consume protein pre or post-workout?

It’s unclear whether there is any major advantage to consuming your protein either pre or post-workout, so to maximize results most bodybuilders do both.

However, for recreational trainees, as long as you consume your protein some time peri-workout (either before or after your training session) and you’re hitting your leucine threshold (more on this below) that should be ample.

If you train in the morning it’s preferable to eat something before your session because when you're training in a fasted state, your body has a weaker signal for muscle growth. Consuming protein pre-workout can help to both increase anabolism (protein synthesis) and decrease catabolism (protein breakdown) in your muscles, resulting in greater growth.

However, if you’re like me and struggle to keep anything down when you eat just before exercising, then it’s fine to have about 20 grams of carbs (a banana will do) to help shift your body from being in a catabolic state into an anabolic state. You can have the harder-to-digest protein post-workout instead when your digestive system is no longer being shut down by your skeletal muscles.

(3) Can you just eat the bulk of your protein at dinner?

Some of the amino acids that you eat aren’t taken up by the liver and are instead shipped out directly to muscle cells. These are known as branch-chained amino acids (BCAAs). The most important BCAA when it comes to the regeneration and remodelling of muscle tissue is leucine.

The intracellular leucine level has to rise sufficiently to reach the required level for muscle protein synthesis to occur. This is known as the ‘leucine threshold’ (which is lowered by exercising because muscular contractions sensitize the muscle cells to the effects of leucine).

In practice, for most individuals, this means consuming a minimum of 0.3 g/kg protein in each meal (where each meal has a complete amino acid profile). So for a 70kg woman, aim for a minimum of 21g of protein per meal.

But, if you’re older, injured, or have a chronic disease such as diabetes the leucine threshold is raised, thereby requiring more leucine to stimulate muscle protein synthesis. This 'anabolic resistance’ can be mitigated by consuming a minimum of 0.4g to 0.6g protein/kg per meal.

So, in these circumstances, the same woman should aim for a minimum of 28g of protein per meal.In effect, if you’re elderly, sick or injured it’s beneficial for your health if you not only consume adequate protein, but spread it out fairly evenly throughout the day.

An 80 year-old man who weighs 80 kg and eats 4 meals a day should aim for a minimum of 34g protein per meal (in order to meet both the leucine threshold and the minimum target of 1.7g/kg/day for an older adult who wants to gain muscle).

Key Takeaways

  1. Consume the majority of your protein during your anabolic window. For novices this lasts for around 72 hours. For advanced trainees this can go down to 24 hours.
  2. For recreational trainees there is no major advantage to consuming protein either pre or post-workout
  3. Ideally, you should eat a minimum of 0.3g/kg of protein with each meal to attain the leucine threshold required for optimal muscle protein synthesis. This increases to 0.4g-0.6g/kg if you’re older, sick or injured.

6. Sources of protein

Illustration of protein-rich foods

So, can you just get all your protein from soy sausages and protein bars? If you care about how healthy and lean you are then, no, it’s not recommended. It’s a good idea to generally go for leaner proteins that are higher in nutrients.

Whole food animal proteins are generally considered to be the best sources of protein due to their high nutrient content.

Milk contains a highly absorbable combination of whey and casein and is therefore considered superior to nut ‘milks’ such as  almond milk which has around eight times less protein.

Also, dairy consumption whilst following a resistance training program, has been shown to positively impact body composition in women by promoting losses in fat, gains or maintenance of lean mass and preservation of bone.

Veggie protein sources are generally less desirable because many plants have a food matrix that negatively affects protein quality. Although, as previously stated, vegans can mitigate this by ensuring they get a complete amino acid profile with every meal and by eating around 20% more total protein than is recommended for omnivores. For optimum results, at least half of your protein requirement should come from high quality protein sources (listed below).

High quality

  • Whole dairy
  • Meats
  • Fish
  • Boiled / baked eggs
  • Poultry
  • Milk protein
  • Casein protein

Medium quality

  • Whey protein
  • Rice, pea, hemp, hydrolysed

Low quality

  • Soy, other veggie sources

If you’re struggling to eat enough protein purely through whole foods, it can be practical to top up your protein intake with either a whey or casein supplement. Whey is preferable either pre or post-workout as it’s absorbed faster by the body. Slower-digesting casein is preferable if you’re consuming it before bedtime.

The main objection to protein powders is that because they contain chemicals like aspartame, they’re not ‘natural’ and must be bad for you. However, as Menno Henselmans explains, once consumed, aspartame is broken down into harmless substances that are found in much higher concentrations in many whole foods.

Key Takeaways

  1. Whole food animal proteins are the best sources of protein due to their high nutrient content.

7. But, what about the planet?

Illustration of a cow farting on Planet Earth

Another objection to a higher protein diet is that it’s bad for the planet. Are your muscles just a sign of you being an egotistical, narcissistic moron who doesn’t believe in climate change?

Fortunately, not.

Unless you eat steak and burgers every day.

As you can see from the graphic below, there are huge differences between the greenhouse gas emissions of different foods. And, surprisingly (at least for me), it’s not because of the distance between your plate and where the food came from.

The most important determinant of the food’s carbon footprint is how it’s farmed. Beef and lamb do not score well. So, if you're concerned about the environment then just replace this pair of ruminants with a combination of chicken, pork, fish, eggs and milk. In doing so, you'll have cut your contribution to the planet’s demise by a factor of ten.

A graph showing greenhouse gas emissions of common foods
Greenhouse gas emissions of common foods

*You get bonus virtue-signalling points for consuming nuts as these actually have a negative land use change score (carbon is stored in the nut trees that are replacing croplands).


Key Takeaways

  1. Eating pork, chicken, eggs and milk is better for the environment than eating chocolate and drinking coffee.
  2. You’ll make the biggest diet-related reduction of your carbon footprint by cutting out beef and lamb.

8. Summary

  1. Protein is the most important macronutrient for weight loss.
  2. Protein doesn't damage your kidneys (unless you already have CKD). And it doesn't weaken your bones (if anything, it's more likely to strengthen them, especially if consumed in the context of an active lifestyle).
  3. A higher protein diet will help you lose body fat due to its increased satiety and higher thermic effect. It will also help you preserve muscle while you’re in the caloric deficit required to lose weight.
  4. You'll need to eat more than the recommended daily allowance if you're active and want to optimise your health (aim for 1.8g of protein per kilo of bodyweight per day).
  5. Whole food animal sources are the best sources of protein and should provide at least 50% of the protein in your diet. Whole milk is a natural muscle builder. It’s ok to supplement with whey and casein given the net health benefits of meeting daily protein requirements.
  6. Plant sources of protein are generally considered inferior to animal sources but vegans can compensate for this by adjusting the amino acid profile of every meal and eating a protein surplus.
  7. If you’re concerned about the effect your diet has on the environment, cutting out beef and lamb will make the most impactful reduction of your carbon footprint (and I hate to say it but cutting down on coffee, chocolate and cheese will make a pretty big dent in it too).