Protein is one of the most hotly debated topics on the internet. Protein plays a unique role in fat loss so it’s important to know the fundamentals, what the scientific studies have said, and where all the different rules of thumb come from.
Why does it feel like noone agrees on how much protein I need?
There’s many different recommendations for protein intake, these recommendations come from different times and different objectives. We’ll first look at some of these recommendations in greater detail later on, but first we will explain what UK and US governments recommend.
In the UK, the Reference Nutrient Intake (RNI) was set in 1991 based on the WHO’s 1985 “Energy and Protein Requirements”, since then it has been set at 0.75g/kg/day for adults 19 and over. Which means a person weighing 80kg requires 60g of protein every day otherwise they would be considered deficient. [Source: Dietry Reference Values – A Guide (1991)]
In the US the Recommended Dietary Allowance (RDA) was set at 0.8g/kg/day for adults 19 and over and published in 1989. That means the same 80kg person is recommended 64g of protein before being considered deficient. [Source: 10th Edition of the U.S. Recommended Dietary Allowance Section 6, specifically table 6-4]
Looking more broadly, most countries recommend around the 0.8g/kg/day amount, but it’s not unheard of for that to stray upwards, including recommendations hitting 1.0g/kg/day or higher in certain circumstances in places including France, Russia, and China.
So I should just follow my country’s advice?
It’s important to remember that those recommendations exist to prevent protein deficiency, not for optimal outcomes in any given situation. You would have noticed that the recommendations are decades old at this point and the reason they don’t get update regularly or more recently is because of their objective of avoiding deficiency, not to provide a subjective ‘optimal’ outcome for anyone. This is often explained in the documents themselves.
“Deciding how much protein or vitamin C or calcium a person should eat for optimal
health is difficult for many reasons, not least because there is no definition of
optimal health.” – Dietry Reference Values – A Guide (1991) Page 2 (page 8 of the PDF)
Well who on earth should I listen to then?
And here lays the crux of the debates on the internet. Protein can benefit people with differing lifestyles in different ways, and these recommendations can cross the borders of lifestyles without any context or clarity. Quite often the figures quoted do have some evidence behind them, but that evidence may bear no relevance to the context they are presented.
Relevant contextulised advice is vital in making an informed decision.
What evidence exists for fat loss scenarios?
First of all some housekeeping: Some recommendations are based on bodyweight, others on lean mass; the implications of that difference deserve their own discussion, in this article we will stick with current bodyweight recommendations due to the ease of understanding, practicalities of measurement, and the consistent decision of researchers to present the data in terms of bodyweight.
There is large number of studies that aim to tackle this question, in 2024 there was a Meta Analysis study (an analysis that combines results from multiple independent studies to produce a single, more precise, conclusion) that looked at forty-seven studies, with over three thousand participants total.
The study titled Enhanced protein intake on maintaining muscle mass, strength, and physical function in adults with overweight/obesity: A systematic review and meta-analysis found that during weight loss, an intake below 1.0g/kg/day is associated with a higher risk of muscle mass decline. Exceeding 1.3g/kg/day is anticipated to increase muscle mass according to this analysis.
Outside of fat loss scenarios and famously, there was a meta-analysis by Morton et al published in 2018, which found what appears to be an upper limit of 1.62g/kg/day to be an upper limit of benefits, the associated figure 5 graph has been widely shared online. Importantly, the context of this analysis is healthy trained individuals, which may not transfer directly to weight loss individuals, it is included here due to the ubiquitous reference to the 1.6 or 1.62 figures in reference to protein online.
Why is it so important whether muscle declines or increases?
The amount of muscle we have not only dictates things like our strength, but also has a measurable effect on our metabolism, and improved body composition. This can help achieve more aesthetic and sustainable results. Given the choice and all things being equal, there are few, if any, reasons to risk muscle loss.
Why don’t I just eat a very high protein diet, more is better, right?
As with all things, there are trade offs and considerations.
Fats and Carbohydrates also play important roles in weightloss and exercise, over emphasising one nutrient over another while following a restricted calorie intake has inherent impacts. For that reason it is important to consider that ‘enough’ is better than ‘optimal’.
In practical terms, during fat loss, consistently eating below around 1.0 g/kg/day is best thought of as a risk you’d need a good reason to take; higher intakes make sense when they’re serving a clear purpose, be that dietry preference, hunger control, or muscle growth.
