The Effects of Underfueling, a.k.a. Not Eating Enough

It might not be surprising that undereating isn't helpful when it comes to building muscle.

What might be surprising, however, is that undereating also decreases Resting Metabolic Rate and impacts hormone levels.   

This study looked at 30 women who were all on the same days of their menstrual cycles.  The study started with all women eating an optimal number of calories (OEA or Optimal Energy Availability) for 5 days.  Then half of the group continued to receive these optimal calories for the next 10 days, while the other half ate lower calories (LEA of Lower Energy Availability).

They were provided with food.  The LEA group ate ~1377 calories per day, while the OEA group ate ~2235 calories.  Protein was high for both, in the neighborhood of 0.7 calories per pound of body weight.

The women had similar levels of fitness going into this study and they did the same workouts over the 10 days.  They did cardio workouts three times per week, and also strength trained three times per week.

What were the results??

"Compared to OEA, daily rates of myofibrillar and sarcoplasmic protein synthesis decreased in LEA. Nitrogen balance also decreased (via an increase in nitrogen excretion) in LEA compared to OEA.

Body weight remained stable in OEA, whereas it decreased by 1.7 kg (3.7 pounds) in LEA. In LEA, fat mass decreased by 1.3 kg and bone-free lean mass decreased by 0.4 kg, whereas in OEA, lean mass increased by 0.4 kg and fat mass decreased by 0.5 kg. Resting metabolic rate also decreased in LEA compared to OEA (−65 kcal vs. no change).

In terms of blood biomarkers, levels of thyrotropin, T3, and glucose decreased, and levels of sex hormone binding globulin increased in LEA compared to OEA."

This image is from the study and summarizes these results:

So, the LEA group lost almost 4 pounds in 10 days (which is a lot for that amount of time!) and some of it was lean muscle mass.  

What's the bottom line here?  

Yes, eating a lower amount of calories can help you lose weight. HOWEVER, chronically undereating can also cause your workout performance and effectiveness to suffer. You may also be messing with your hormones and metabolism, and you may also lose lean body muscle mass *even if* you're eating enough protein.  This is not good!  We want and need lean muscle mass!! 

So, this study underlines the fact that if weight loss is your goal, ideally we'd find a calorie intake total that is just slightly below maintenance to allow for sustained weight loss that doesn't also cause you to lose muscle or impact your hormones.

If you would like help discovering what that calorie total is for you, how much protein you need, and what workouts might help you achieve your desired body composition, please reach out! Click here to schedule a call to talk further!

As always, thank you for reading,
Sara