Hello,

in 2013, I was 95kg (183 cm), had stop sport years ago (I was 47).

I began to ride bike again (had done that younger, regional competitions) once, then twice, then 3 times a week.
In one year went down to 85kg, while gaining muscles.

I began track cycling competition, moving down to 80kg, while still gaining a bit more muscle.

Then I began triathlon one year ago, moving down to 77 kg, gaining muscle mostly up body (from swimming).

Not really impressive lost of weight, but progressive, without real pressure on calorie intake.

The most important : began with a lot of base endurance (around 40% of PMA)
Even for a high level athlete, 80% is endurance work. For a beginner, I would say 90 % of base endurance. Hours and hours of base endurance. Your body will burn fat instead of sugar (at 60% PMA, your body draw as much energy from fat than from carbohydrate, while fat reserve are much much bigger, and more energy efficient). It will train your slow twitch fibers (the one you really need here), and reduce your weight.

Another big thing : running is the most difficult, because it destroy muscles and tendon (I'm now 52...)
It is easier to train hours and hours cycling and swimming (no harm), and increase very slowly your volume in running, finding the right gait, shoes, adapting very progressively the muscles and tendon, solving issues when they arise (sure, issues arise when volume increase).

I'm not a medic, neither a coach or a nutritionist, just talking from my own experience, and some other peoples I know experience.

I believe it, because I watch football sometimes and those guys can freaking move, but that's still an astonishing time for a 1/2 given the weight it was done at.

That half marathon time is already 6 years old, I was around 110kg / 245lbs then. Haven't run one lately though have one planned March '19.

Fellow big lad here... 194cm (6'4"), 125KG, reformed rugby player.

I've done all distances up to and including Ironman. Always struggled with my weight simply for being a glutton, although I was probably at about 115KG for both my IMs. Tri PBS are course dependent but..

Sprint about 1.15
Oly about 2.30
70.3 about 6.15
IM 13.40.
1/2 Marathon 1.50
10K 50:12
5K 24.32

I'm a much better swimmer than runner. Average cyclist. If I took an average split position across every tri (regardless of distance) I am usually to 5-10% in the swim, upper 40% on the bike and bottom 30% on the run.. if that makes sense.