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How low should you take your calories? When cutting calories can begin to backfire...Updated a month ago


We all work with clients and people in achieving their goals on the path to becoming a better version of themselves. For many people, this means helping them achieve weight loss. But simply losing weight or, in other words, watching the number on the scale when we step on it get lower and lower is not what we are ultimately after. We need to educate and help people lose fat. The greater the proportion of fat that someone loses, the higher the quality of weight loss. Alternatively, the higher the proportion of lost weight that is lean tissue or fat-free mass, which is predominantly skeletal muscle tissue, the lower the quality of weight loss.

Why does quality of weight loss matter if all you want to do is lose the belly or fit into a favorite pair of jeans? This answer is mostly two-fold. First, your metabolic health as people with more lean tissue maintain higher metabolic rates. Second, your ability to move, function, and do things is typically higher with more lean tissue. This will not only enable you to do more of the things you want to do, but also help you avoid injuries, falls, etc.


Three pillars! To maximize fat loss, this is where someone needs to focus:

A) create a caloric deficit,
B) add resistance training, and
C) increase the proportion of protein in one’s diet

The entire focus of this article is on the first point: caloric deficit. Simply put, if you want to lose weight, you must, on a consistent basis, expend (burn) more calories from exercise and physical activity than what you consume in your diet. Next, add a very basic resistance training stimulus. In fairness, we aren’t really sure if five days (or more) per week is better than two days per week to help you maintain your amount of muscle mass, but we do know that 2-3 days per week of performing at least one resistance training exercise per major muscle group with a challenging intensity for 8 – 12 repetitions can function as a minimum. Of course, you likely need to exercise more than this as the exercise will contribute to creating a caloric deficit, but some part of your exercise must include resistance training if you want to achieve high-quality weight loss. The final point is increasing the proportion of dietary protein consumed in your diet. Again, like resistance training, science hasn’t really honed in on what is considered to be a minimum and maximum, but my guess is that somewhere around 2 – 3x the RDA (which is currently 0.8 grams of protein per kilogram of body mass per day) will get the job done. So a ballpark “back of the napkin” recommendation for daily protein intake is 1.6 – 2.0 g/kg/day. Now, most of us North Americans don’t really speak in kilograms, so somewhere close to one gram per pound of body mass will put you on the upper half of this range.


A point exists where cutting calories to a greater and greater amount becomes harmful. This may seem like common sense, so the key question this article will discuss is, “How much of a caloric deficit is too much?” Before we jump more into this question, we must briefly review the basics of weight loss and this starts with the realization that a caloric deficit must be achieved for weight loss to occur. While other factors exist that can further impact weight loss, achieving and maintaining a caloric deficit is the most significant and important factor to predict body mass reductions.

A caloric deficit is achieved through manipulations to how many calories someone consumes in their diet and how many calories someone burns as part of physical activity and exercise. While it is numerically possible to achieve a greater calorie deficit by increasing the amount of exercise you complete each day, most people accept that there are limits to this approach simply due to the amount of time spent exercising as well as the eventual stress and toll this approach will take on your body. Put simply, “you can’t outrun a diet with excessive calories.” Alternatively, this should lead us to the realization that the most consistent change a person can typically make to achieve a caloric deficit is through reductions in their caloric intake.

Now that these bases have been covered, what is our most critical question? How much of a deficit is too much?

From a scientific perspective, a review article completed by Murphy and Koehler (1) reviewed the results of different research studies and evaluated how strength and lean mass changed with different amounts of calorie deficit. They only included studies that lasted for at least three weeks. Why just three weeks? Well, for starters, research like this in people is very challenging and participants typically are not able to sustain compliance for prolonged periods of time. Sounds familiar, right? Diets and restriction are hard and take their toll, and eventually you slip back on the process?


Their results indicated that as the amount of calorie deficit became greater (they ate less and exercised more), the more muscle they lost. As a skeletal muscle lover, I can say this is not a good thing. We need healthy muscle for so many things that stretch way beyond looking good with your shirt off or in a bathing suit.


The interesting thing about this paper was that they attempted to identify if a point existed where a greater calorie deficit led to negative changes or loss of muscle mass. The authors reported that a calorie deficit of greater than 500 calories per day consistently led to muscle mass and that a greater deficit beyond this point led to greater amounts of muscle mass being lost. So a deficit greater than 500 calories per day seems to serve as a threshold of sorts where going beyond it leads to negative outcomes.

Energy Deficit Table

The other thing this tells us is that achieving a smaller calorie deficit of 100 – 300 kcals/day may still lead to weight loss (yes, it will be slower), but you will be able to maintain or maybe even gain a little bit of muscle mass in the process. And this is something nearly everyone would be happy with.


Weight loss occurs when we achieve a caloric deficit. Stop eating, add some exercise and you will lose weight, but drastic caloric restriction will increase how much of the weight that you are losing is muscle. Not good! So to maximize fat loss, a caloric deficit must be added with a resistance training program and a restricted calorie intake diet that is leveraged towards increased amounts of protein. A good starting point is around 1 gram of protein per pound of body mass. Make that your goal and try to get as close to it as possible. Going above shouldn’t be a goal. Finally, research suggests that a daily energy deficit that doesn’t exceed 500 calories per day can help to make sure that maximal amounts of fat are lost.


Chad Kerksick is currently an Associate Professor of Exercise Science and Director of the Exercise and Performance Nutrition Laboratory at Lindenwood University. Dr. Kerksick earned his PhD in Exercise, Nutrition, and Preventive Health in 2006. Since that time has worked as a university professor teaching classes and conducting research in areas related to exercise and nutrition. His laboratory, the Exercise and Performance Nutrition Laboratory (www.lindenwood.edu/EPNL), conducts rigorous, high-quality research investigations devoted to examining the impact of exercise and nutritional interventions of health, performance, and recovery of a large number of populations. Chad has worked with 1st Phorm since 2010 providing educational content in multiple formats, assisting with educational events, and providing feedback for formulations and labeling.


1. Murphy C, Koehler K. Energy deficiency impairs resistance training gains in lean mass but not strength: A meta-analysis and meta-regression. Scand J Med Sci Sports. 2021.

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