Our mission at BodyStats is to make advanced health tracking available to everyone. Part of that is sharing what we find: not just the report in your hand, but the patterns that show up across thousands of customers.

When someone comes back for a second, third or tenth scan, we can watch how a real body changes over a diet. This article looks at what happens the longer a diet runs, and why a scan after many months of dieting can go the “wrong” way.

The short version

Fat loss is fastest in months 1 to 2 (about 2.8 lb a month for the typical man, 2.0 lb for the typical woman) and slows to about half a pound a month after six months.

Early in a diet, fat almost never goes up between two scans (2% of men). After six months it happens to about 1 in 4 men (23%), and 14% see fat go up while fat-free mass goes down at the same time.

Women are steadier: 13% see fat go up after six months, and 7% see both.

For the typical dieter, fat-free mass barely moves: about 0.2 to 0.3 lb a month.

What we did

We took every BodyStats customer with two or more DEXA scans on our Hologic scanners (Gastown and Toronto), up to October 30, 2026: 2,867 people and 8,180 scans. From each timeline we found the diets: stretches where fat mass dropped from one scan to the next and stayed below where it started. 1,928 customers had at least one (1,159 men and 769 women), giving 1,985 diets and 3,379 scan-to-scan changes, each converted to a per-month rate.

The first 30 days of every diet are left out. Early weight loss is mostly water and stored carbohydrate, not tissue.
A diet ends when fat mass climbs back above where it started. Full rebounds aren’t counted as dieting.
Hologic scans only. Our Yaletown clinic uses a GE scanner, and scans from other clinics are left out, so every comparison is like with like.
Fat-free mass, not “muscle”. DEXA measures everything that isn’t fat: muscle, water, stored carbohydrate, food in the gut, organs and bone. A drop in fat-free mass can be muscle, but it is often water and glycogen.
Median and mean. The large number is the median (the typical customer); the small “AVG” is the mean, which outliers can pull.

Men: fat and fat-free mass, month by month

1,159 men, monthly change while the diet was still running:

Months	Δ Weight	Δ Fat	Δ Fat-free mass	n
Month 1 – 2	−3.4lb avg −3.5	−2.8lb avg −3.6	−0.3lb avg +0.1	327
Month 2 – 3	−2.3lb avg −2.9	−2.3lb avg −2.6	−0.2lb avg −0.2	365
Month 3 – 4	−1.8lb avg −2.1	−1.4lb avg −1.7	−0.3lb avg −0.3	320
Month 4 – 6	−1.1lb avg −1.4	−1.0lb avg −1.2	−0.2lb avg −0.2	403
Month 6 – 9	−0.8lb avg −0.8	−0.6lb avg −0.2	−0.2lb avg −0.7	404
Month 9 – 12	−0.1lb avg −0.1	−0.3lb avg −0.2	0.0lb avg +0.2	184
12+ months	−0.3lb avg −0.4	−0.4lb avg −0.5	0.0lb avg +0.1	181

Median male fat and fat-free mass change during weight loss, month by month, across 1,159 BodyStats customers.

Fat loss is fastest in the first two months and slows every month after. By months 6 to 9 the typical man is losing about half a pound of fat a month, and after nine months it’s down to a few tenths. Fat-free mass drifts down by about 0.2 to 0.3 lb a month, small enough that in any one month it can be hydration rather than muscle.

Women: fat and fat-free mass, month by month

769 women, same method:

Months	Δ Weight	Δ Fat	Δ Fat-free mass	n
Month 1 – 2	−2.1lb avg −2.6	−2.0lb avg −2.5	−0.2lb avg −0.2	151
Month 2 – 3	−1.3lb avg −1.7	−1.5lb avg −1.6	+0.1lb avg −0.1	182
Month 3 – 4	−1.0lb avg −1.5	−0.9lb avg −1.3	−0.1lb avg −0.2	201
Month 4 – 6	−0.9lb avg −1.3	−0.9lb avg −1.1	0.0lb avg −0.2	225
Month 6 – 9	−0.5lb avg −0.9	−0.5lb avg −0.8	−0.1lb avg −0.1	224
Month 9 – 12	−0.5lb avg −0.9	−0.4lb avg −0.5	−0.1lb avg −0.4	95
12+ months	−0.3lb avg −0.4	−0.3lb avg −0.4	+0.1lb avg 0.0	117

Median female fat and fat-free mass change during weight loss, month by month, across 769 BodyStats customers.

Same shape, gentler slope: about 2 lb of fat a month at the start, under a pound a month after four months. Fat-free mass stays close to zero in almost every stretch.

When diets run long, results get less predictable

The typical numbers hide something many long-term dieters run into. Here is the share of scan-to-scan changes where fat went up by more than half a pound a month, and where fat went up while fat-free mass went down at the same time:

Months	Men: fat up	Men: fat up, fat-free down	Women: fat up	Women: fat up, fat-free down
Month 1 – 2	2%	2%	1%	1%
Month 2 – 3	5%	4%	8%	5%
Month 3 – 4	10%	7%	8%	3%
Month 4 – 6	13%	7%	11%	7%
Month 6 – 9	21%	13%	13%	8%
Month 9 – 12	27%	13%	16%	7%
12+ months	24%	16%	10%	6%

In the first two months, almost nobody’s fat goes up. After six months, about one in four men sees it rise between scans, and roughly one in seven sees fat up and fat-free mass down together: the result that feels most like the diet “stopped working”. Women see it about half as often.

Some of this is real: long diets bring more hunger, less energy for training and more slips, and a body that has been in a deficit for months holds on harder. Some of it is measurement: after months of low carbohydrate intake, a single refeed or a change in water can move fat-free mass by a few pounds, and DEXA reads it. Either way, if you have been dieting for six months or more and your latest scan went the wrong way, you are far from alone.

Our founder went through this himself. In 2023 he lost 50 lb in four months, then kept pushing, and his next scans showed most of the extra weight coming from fat-free mass rather than fat. He wrote about it in The Dangers of Over Dieting: My Journey.

What to do if your scan goes the wrong way on a long diet

Check the scan conditions first. Same time of day, same food and water beforehand, no hard training the day before. Our preparation guide covers it.
Look at the trend, not one scan. Two or three scans pointing the same way tell you much more than one.
Look at your training log. If your lifts are holding or going up, a drop in fat-free mass is more likely water than muscle.
Talk it through. Book a free 30-minute virtual consult from your dashboard at bodystats.ca/results (choose Schedule Consult), and a technician will go through your scans with you.

What this data can’t tell you

Customers who come back are an engaged group. They likely train and eat more deliberately than the average dieter.
We don’t have food or training logs. We can see what changed, not why.
“Dieting” here means fat mass going down, not a planned deficit or a coach’s program.
Read the median first. The mean moves with a few extreme readings, especially in the smaller groups past nine months.

Updated October 30, 2026. We refreshed this article with five more months of scans and rechecked it. The first version (May 2026) included scans from our GE scanner and from other clinics, and labelled fat-free mass as “muscle”. Together those made it look as if the average man regains fat and loses over a pound of muscle a month after six months of dieting. On Hologic scans alone, that average doesn’t hold; the steady finding is the one above: fat going up becomes much more common the longer men diet.

Our mission is to make advanced health tracking available to everyone. That includes the knowledge we gain along the way.