How Much Protein Do You Need When Losing Weight?
The holy grail of weight loss is shedding fat without losing any muscle. You may have heard that the solution to this delicate dance lies in downing tons of protein. Is this true?
It turns out that our bodies generally do a good job of tapping into our fat stores when we are in a calorie deficit. After all, that’s their raison d’être! On average, 70–90% of weight loss comes from body fat (a mix of visceral and subcutaneous adipose tissues). The rest comes from things we’d rather hang onto, known as “lean mass”, “fat-free mass” or “FFM” (water, muscle, organs).
Can eating more protein help us tip the balance towards more fat and less lean?
Intuitively, this makes sense. After all, our muscles are largely made of protein, and bodybuilders build more muscle when they pound protein shakes. If we’re hanging onto muscle, then we should be losing fat, right?
When you dig into the data, it quickly becomes apparent that things are not as simple as “the more protein the better”. This article shares some of the science on how your weight loss quality — fat vs lean tissue — is affected by dietary protein, to help you set your optimal protein target.
Weight Loss Quality vs Quantity. This article focuses on body composition changes, not on total weight loss. Check out “Which Weight Loss Diet is Best” for my review of the science on overall weight loss.
Spoiler alert: What matters most for total weight loss is our ability to sustain an energy (calorie) deficit. There is no magic macronutrient mix (protein vs carbs vs fats).
How much dietary protein is ‘enough’?
Before diving into weight loss studies, let’s set the stage by defining how much protein is deemed enough in normal life.
Most nutritional guidelines around the world recommend roughly 0.8 g/kg (0.36 g/lb) protein for adults. This number, the Recommended Daily Intake (RDIs), tells you how much daily protein should meet the needs of most (97–98%) people. Protein needs are higher in certain people and situations, such as in those who are rapidly growing or repairing tissues. Read more here about the science behind protein needs.
Calculate Your Basic Protein Needs:
A 60 kg / 132 lb adult needs 48 grams protein daily based on:
60 kg x 0.8 g/kg or 132 lbs x 0.36 g/lb
It’s worth noting that standard protein guidelines are based on non-obese adults and may be lower for those with a higher percent body fat because fat is not as metabolically demanding as muscle and organs. If I gained 10 kg of muscle, I would need 8 grams more protein per day to maintain my extra mass, whereas, if I gained 10 kg of body fat, this would not be the case.
Low protein diets
Most weight loss programs are formulated to ensure that subject meet their basic protein needs. Thus, data on low-protein diets are sparse.
Our best source of insights are ultra-low calorie diets, because it can be hard to cram enough protein into a few bites of food.
Studies comparing diets that are low in protein to those that provide just enough tend to find less favourable body composition changes when protein is is inadequate — notably, greater loss of lean tissue relative to fat. The magnitude of this effect varies from subtle to noteworthy.
This 2016 study of 57 overweight or obese adults compared subjects on a standard low calorie diet (1250 calories per day, 1.0 g/kg protein) to those on a very low calorie diet (500 calories daily, 0.6 g/kg protein). Both groups lost about 7 kg of weight, though those who slashed calories hard hit this target more quickly. The lower protein group lost slightly more lean muscle (1.2 kg vs 0.6 kg) than the normal protein group. The normal protein group lost a smidge more body fat, but differences were barely detectable.
This 2008 study of 70 postmenopausal women followed women consuming variable amounts of protein over 20 weeks, during which they cut dietary calories by about 400 calories per day. Some also added exercise. Subjects lost an average of 11 kg of weight, of which roughly two thirds was fat stores.
As shown in the figure, there was a trend, albeit messy, towards greater loss of lean muscle in those who consumed less protein, independent of exercise.
High protein diets
SStudies comparing high protein to normal protein diets have yielded inconsistent results.
As a starting point, it’s useful to look at meta-analyses — studies that synthesize findings across studies. Boosting protein above normal levels tends to either show no effect, or a slight benefit — greater lean sparing and fat loss.
This 2016 review and meta analysis of the effect of protein intake in weight loss studies on older adults reported a moderate win for high protein diets. On average, those on higher protein diets lost 400–800 grams less lean muscle (1–2 lbs). Results from this review, however, should be taken with a grain of salt. Only four of the twenty studies included were considered “low risk” of bias, the rest were “uncertain”, based on their study designs.
Let’s drill down to get a sense of the numbers in different contexts.
This 2012 study of 132 obese men and women didn’t find any differences in quality or quantity of weight loss when comparing a high protein (1.1 g/kg) diet to a normal protein (0.7 g/kg) diet.
Likewise, this 2005 study of 100 obese women found no significant differences in both amount and quality of weight loss between a high protein (~1.1 g/kg or 31% of calories) to a normal /low protein diet (~0.7 g/kg or 18% of calories from protein). Subjects consumed roughly 1300 calories per day over 12 weeks. Both groups lost about 7.3 kg (16 lbs) total, of which about 1.5–2 kg (3–5 lbs) was lean tissue.
This 2014 study of 43 overweight and obese men compared low calorie diets (750 calorie deficit) containing either high protein (1.4 g/kg) or normal protein (0.8 g/kg) diets. The macronutrient distributions were 25:60:15, and 25:50:25 percent energy from fat, carbohydrate, and protein, respectively. Over the course of twelve weeks, both groups lost comparable total weight (10 kg/22 lbs) and body fat. The high protein group lost a little less lean body mass than the normal group (~2 kg vs 3 kg).
This 2003 study of 24 pre-menopausal women examined body composition changes during 10 weeks on a 1700 calorie diet. Subjects were assigned to either a high protein diet (1.5 g/kg) or a normal protein diet (0.8 g/kg) — where carbs replaced protein. Both groups lost around 7 kg of body weight. Those who cranked up the protein (nearly doubling the RDA) lost a tad less lean muscle (0.9 kg vs 1.2 kg) and more fat (5.6 kg vs 4.7 kg) relative to those who consumed normal protein.
Bias Alert! It’s important to always be on the lookout for potential biases. Be sure to check the funder and look for dubious study designs and headlines that may not fully reflect the true results. Anything other than double blind randomized controlled trials can be …subject to interpretation. The protein literature is full of studies funded by those highly invested in a certain outcome (such as the Cattlemen’s association), so be on guard for pro-protein spin!
The Bottom Line
The reality is that those who are overweight or obese will typically come out ahead on body composition — and health — no matter which path to weight loss they take.
Thus, my bottom line on protein intake and weight loss aligns with this 2017 review which recommends “adequate but not excessive” protein (at least 0.8 g/kg). In other words, be sure to cover your bases, but don’t feel that you have to go nuts for protein if it doesn’t suit you.
Whether or not to boost protein intake beyond your basic protein needs is a personal question. While there many be a modest shift towards more fat loss relative to lean tissues, the effects are variable and modest, even when protein intake far exceeds the normal recommended intake.
Getting enough protein is normally a piece of cake on just about any varied diet, but can be challenging when we cut calories. While a few hundred calorie deficit isn’t a big deal, packing in a whack of protein on a meagre calorie budget isn’t so easy. If you do severely restrict calories, you’ll need to dial up protein rich foods and dial down low protein foods to meet even your basic needs.
When consuming my typical 1800 calories per day, I can effortlessly hit my 48 grams of protein. All it takes is 11% of my total calories from protein — a level that I can easily get just from whole grains. To hit those same 48 grams on a calorie-reduced diet (e.g. 1200 calories) I need to get 17% of my total calories from protein — a level that requires much more thought and planning.
It’s worth mentioning that diet is just one of the many factors that impact our ability to preserve lean muscle during weight loss. Other factors include those we can readily toggle — like physical activity, and rate of weight loss, and those that we can’t, like age, physiology, and more.
All told, this research expedition reinforced my feeling that we are focusing too much on seeking an optimal nutritional formula for weight loss, and not enough on tweaking our eating plan to our preferences, our biology, and our lives.
In my books, there is no one best diet, only your best diet. Your winning diet is the one that that meets your basic nutritional needs while keeping you feeling satisfied without overeating. Check out my “Less is More Lifetime Diet” for tips on doing just this, without going hangry.
I am formally trained in human genetics (PhD) and spent the first decade of my career working in cancer research, drug development, and personalized medicine. I love being active, eating veggies, playing games, and talking nerdy.
My new career chapter is dedicated to empowering others to make well-informed healthy choices that they truly enjoy.
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