The phrase "are much leaner" is correct and usable in written English.
It can be used when comparing the body composition or physical condition of two or more subjects, indicating that one is significantly less fat or more toned than the other.
Example: "After months of training, the athletes are much leaner than they were at the beginning of the season."
Alternatives: "are significantly slimmer" or "are considerably more toned."
Wild geese, one of the North American hunter's great prizes, are much leaner and chewier in texture than domestic geese; they work off their fat in flight.
The soldiers, mostly ground troops, are much leaner than Tom Cruise was in that 1986 film, though they grin just as righteously.
So when Will Self talks about suddenly being able to fit all the financially viable British authors into a spare bedroom, rather than the larger reception room of yore, readers can also imagine that the poorer writers among them are much leaner, making more space for the rounder, well-heeled, well-lunched variety.
In 2013, the subsequent weekend saw Man of Steel reboot the market, followed later in June by World War Z and Despicable Me 2. There are much leaner pickings on offer in June this year, due to World Cup football, and this weekend UK film distributors are being exceptionally cautious.
Now he jokes that he's reached an age when the pickings are much leaner, with Morgan Freeman monopolizing the good parts that do come up.
Autopsy revealed that Lmod3 PB/PB mice are much leaner than wild type (Fig. 2A).
Wales were much leaner, more athletic and prepared to play at pace.
Without grain, the beef is much leaner -- but it is also less tender until it is hung.
But it was also a set of songs in particular, which were much leaner and stronger than those on "13".
BP is much leaner (and cheaper) than it was in the era of what now seems like reckless expansion under Lord Browne and Tony Hayward.
He is much leaner than Moses, who has retired as a hurdler and as a bobsledder, which was his more recent endeavor.
