Does Too Much Protein Make You Fat?

Beau Scott BSC of Sports Biomedicine and Nutrition at Cardiff Sports Nutrition

Protein is an essential nutrient that plays important roles in many functions throughout the body, and not just for building muscle. Protein provides the essential and non-essential amino acids that serve as the building blocks for other proteins, enzymes and hormones within in the body.

Insufficient intake of protein in the diet leads to the body breaking down its own protein, usually the muscles, in order to meet the minimum demands of essential function.

UK the recommended

In the UK the recommended daily protein intake for adults is set at 50g by the NHS, or 0.75g per kilogram of bodyweight by the British Nutrition Foundation.

These guidelines are the MINIMUM requirement needed for essential bodily processes and functions and does not take into account the level of exercise an individual may participate in.

For people who participate in regular exercise, their protein intake is significantly higher, particularly for those undertaking resistance training with the goal of building muscle. Protein intakes of 1.5g-3g per kilogram of bodyweight have been rigorously studied to find the optimum quantity, with 2.4g per kilogram being the most often cited to meet minimum requirements and provide the extra protein needed for muscular growth and repair.

When compared to the guidelines for a sedentary person, an 85kg male would go from 64g of protein per day to 204g. As we can see this is a very large increase, but can we eat too much protein?

When it comes to protein consumption, particularly with regards to protein supplementation, there are many rumours about negative health effects caused by over consumption. Rumours that state over consumption of protein could cause kidney failure, or that the body can only digest 30g of protein per sitting.


Both of these rumours either have no or very questionable scientific basis behind them, and have been disproved many times over.

Another rumour that has recently gained significant traction as a result of high protein diets is that consuming too much protein could lead to an increase in fat gain.

But is this really the case?

Is this every bodybuilder’s, weight trainer’s or athletes worse nightmare, that if we eat too much protein we will get fat?

Simply, no.

The Theory

The theory is that once energy and protein requirements are met, excess amino acids or proteins are then stored as body fat.

However, a recent study by Bray et al (2012) set out to test this hypothesis and found it to not to be the case.

They tested three groups with varying protein intake, low (47g or 0.68g/kg), medium (140g or 1.79/kg) and high (230g or 3.0g/kg).

Each group was fed 1000kcals above their maintenance level, where carbohydrate intake was kept constant at 41-42% of daily calories, and dietary fats were adjusted to reach the 1000kcal threshold for each group.

At the end of the study the researchers found that there was little difference in the level of fat gain between each group, with the high protein group actually showing a slightly lower increase in fat mass.

What the experiment did show, however, was that the medium and high protein groups did gain an average of 3kg more lean mass (not fat mass) than the low protein group.

This shows that although the medium and particularly the high protein group over consumed protein, only an increase in lean body mass was observed, not in fat storage.

It should also be noted at this point that the study was not performed with any resistance training regime that could explain the increase in lean mass. The body fat increase that was experienced by all three groups was therefore shown to be as result of excess total calories and not protein intake.

Whereas, protein contributed to changes in lean body mass, and not fat mass.

The body does have the correct pathways

The body does have the correct pathways to convert excess proteins into fatty acids, but they are so limited that it only happens at a very small capacity.

This is further reduced by the fact that only two out of 20 main amino acids, leucine and lysine, contain the correct carbon backbone that is needed for them to be converted into fatty acids.

This process also requires more energy than it actually provides, so is therefore only beneficial to the body under extreme circumstances.

various protein sources

With all these points significantly hindering the process, it makes it extremely unlikely that protein will be converted into fat stores under normal dietary circumstances where energy requirements are easily met.

In fact, most fat loss diets are based on high quantities of protein with far lower quantities of fats and carbohydrates due to this poor conversion rate, where fat stores will be used for energy and not dietary protein.

The myth surrounding high protein consumption with fat gain may be attributed to the increase in lean mass, and therefore total body mass, leading some people to incorrectly assume that this additional weight was added on solely as fat stores.

Weighing Scales

We should all know by now, that the figures on the weighing scales aren’t the best method to accurately measure fat loss, muscle is after all denser than fat. The above study not only disproves the myth of high protein fat gain, but also shows how it is an effective way of increasing lean mass.

However, the result from this study should not be misinterpreted, a consumption of excess calories from any source will still lead to fat gain, this is not an excuse to go and eat your bodyweight in steak!

A consumption of, for example, 10,000 calories from protein would still lead to a gain in body fat as you would be consuming 7,500 calories more than what an average person needs to function.

This would be due to the total level of calories rather than from the source, as the study suggested, especially if there was a lack of dietary carbohydrates or fats, forcing your body to use these pathways. This is an extreme example and under normal dietary circumstances, where energy and glucose needs are met, fat gain from high levels of protein is extremely unlikely, as the study showed.