How much body fat can women lose in 10 days? Is muscle mass affected? Here’s everything you need to know.
Want to lose 3 pounds of fat in only ten days? There’s a diet and training plan for that. It’s even “science-based.”
But what if that same plan caused you to lose some muscle while impairing your thyroid function and metabolism? Still worth it? Probably not. Muscle loss paired with fat loss, accompanied by a drop-kick to the metabolism, usually leads to a smaller but flabbier body. And you’ll regain the fat anyway.
But there may be a way to fix this 10-day diet, losing the same amount of fat (or close to it) while retaining muscle, keeping your hormones healthy, and not buggering up your metabolism. First, let’s look at the original study on this aggressive plan, then we’ll make it better.
Researchers recruited 30 weight-lifting women with a body fat percentage of 24% and divided them into two groups:
Based on the energy availability formula, this group consumed 2400 calories per day (50 kcals/kg FFM). This means they ate enough to maintain body weight and fuel their workouts. Their daily macro breakdown looked something like this:
Protein: 100 grams
Carbs: 310 grams
Fat: 80 grams
This group consumed 1350 calories per day (25 kcals/kg FFM) – a big 45% caloric deficit. Their daily macro breakdown looked like this:
Protein: 100 grams
Carbs: 145 grams
Fat: 40 grams
Both groups were supplied with food and put on a supervised weight training program: two upper and two lower-body days. They also did cardio on two of those days: one day of intense intervals and one easier, longer session. They took one off-day per 5-day cycle and went through the whole shebang twice.
The women underwent a lot of blood tests, DEXA scans, tests of resting metabolic rate, muscle protein synthesis testing, and quizzes to identify their love language. (I may have made one of those up.)
Here’s what happened to each group after ten days:
- Muscle Protein Synthesis: Increased. This indicates trending muscle gains.
- Body Composition: Muscle mass increased by about 1 pound. Body fat decreased by just over 1 pound.
- Resting Metabolic Rate: Slightly boosted (by 14 calories).
- Thyroid Hormone: No change.
- Muscle Protein Synthesis: Decreased. This indicates trending muscle loss.
- Body Composition: Muscle mass decreased by about 1 pound. Body fat decreased by 3 pounds.
- Resting Metabolic Rate: Impaired (by 65 calories).
- Thyroid Hormone: Significantly decreased.
While the aggressively dieting group did lose two more pounds of fat than the other group, they also lost muscle and sucker-punched their metabolic rates and thyroids.
On the flip side, the maintenance-calorie group gained some muscle, didn’t throw a monkey wrench into their metabolic rate or thyroid health, and still managed to drop a little fat. (I’m guessing that even though these were experienced lifters, the supervised training was more challenging than their usual workouts, so they lost fat on what researchers thought were maintenance-level calories.)
Remember, all of this happened in just ten days. Extend this plan over a few months and the low-calorie group would be in a world of metabolic trouble. The optimal calorie group, however, would be hotter.
A 10-day diet is appealing. Could we fix the problems and make it work? Well, if you’re determined to try it, here’s what T Nation contributor Bill Campbell, PhD., recommends:
Keep the strict 45% caloric deficit and training program.
Make it a 9-day diet. Diet for 4 days, then return to maintenance calories on the 5th day (a refeed, not a cheat day). Then, diet again for 4 days. Dr. Campbell says this will prevent muscle loss. This is basically like the plan outlined in my Non-Linear Diet for Lifters article.
Increase protein intake to 1 gram per pound of body weight. Reduce fats and carbs to make room for it. I recommend MD Protein (on Amazon) because it contains micellar casein, which stimulates metabolic rate while being anticatabolic.
Those changes should fix the drawbacks while still allowing for some pretty impressive results in a short amount of time. Just make sure you’re not prone to disordered eating tendencies. A 45% deficit is harsh. Don’t let it be the start of an unhealthy starve/binge pattern.
You could just be more patient and use a modest calorie reduction for longer, something like a 25% deficit, which isn’t going to screw up anything as long as you’re eating lots of protein and lifting weights.
The real take-home message? Women can lose fat, build muscle, and ultimately get the body they want by following the optimal calorie plan.
Note: Thanks to smart-guy Bill Campbell and his smart-guy newsletter, Body by Science, for pointing out this study.