One of the questions I get asked most often (by men) following a DEXA scan is: “what percentage body fat do I have to be before I see my abs?”
One of the commonest rule-of-thumb responses is ten percent. But like a lot of stuff to do with the body, it depends.
Look at this scan report for Dave, who has put on both fat and muscle in 12 weeks and now stands at 17.2% fat (subtotal). Moreover, he is 17.5% fat in the trunk and 20% in the belly (android) region. But the photos above show he has respectable (certainly noticeable) abs at the front despite being able to pinch at least an inch at the side.
Compare that to Peter, whose progress we have charted before and whose DEXA fat figures are just 13.7% (subtotal), 13.1% (trunk) and 16.1% (belly) and whose abs remain elusive (sorry, we didn't take a photo).
Dave says he’s just blessed with good, thick abs and works them hard by adding weights to exercises such as hanging leg lifts and incline crunches. He's not in the camp that believes abs don’t need their own workout; he will usually train them hard twice a week.
A quick look at the pair’s respective lean mass index (lean mass divided by height squared in the Lean Indices table on the first page of each report) shows up significant lean mass/muscle differences: 23.6 for Dave, 21.5 for Peter. That 2.1 is a big difference for an index where 19.5 is average and 25 is steroid territory.
Further, relying on body fat percentage doesn’t really make much sense because it’s just an average over your entire body. You might carry your fat atypically. And you can have a low percentage (or proportion) of fat but still be carrying a lot of it in terms of kilos. That's what your fat mass index will make clear.
So it seems that to see your abs you need one or more of: a low FMI, low percentage fat, high LMI, a good ab routine and genetic luck!
Between January and August (2015), more than 350 men and 150 women came for a DEXA scan at Bodyscan’s London location.
The aggregated results are available here and show something quite interesting. The median value for fat mass is almost identical - 16.8kg for men and 17.3kg for women.
Of course, women are typically lighter than men so 17kg of fat will equate to a higher body fat percentage for women. Indeed, the median weight and fat percentage for Bodyscan clients turned out to be:
Men: 83kg weight, 21.8% fat*
Women: 63.1kg, 30.1% fat*
It’s important to remember that Bodyscan clients are not a random sample of the UK population; they have elected to have a DEXA scan for whatever reason (fitness or fat loss) and are probably geographically close to London. The data also include a broad range of ages (the median age is 36 (men) and 35 (women)).
However the approximate 17kg for median fat mass for both sexes is, if nothing else, quirky!
*Note: The data points in the data tables should be all read independently of each other - one should not expect to be in the same percentile for all data points. That’s why the median figures above (21.8% of 83kg for men and 30.1% of 63.1kg for women) do not produce the median fat mass figures of 16.8kg and 17.3kg.