Kate mingled with athletes competing at this summer's Olympic Games in Brazil at the dinner, which featured English asparagus, fillet of beef and an orange-and-chocolate pudding and was held in a more lavish setting than past events.
Almost two-thirds of the British team from the 2012 London Olympics were recipients of the charity's support. Alumni include Jessica Ennis-Hill, runner Mo Farah, diver Tom Daley, cyclist Chris Hoy and paralympic swimmer Ellie Simmonds.
"With little over 50 days to go until the Games begin in Rio, the next Olympiad is almost here," Kate said. "As we did in London in 2012, we will see a new generation of sporting stars emerge into the spotlight."
"This is a little bit more personal and intimate and an indication of how that passion has grown," CEO of the charity Tim Lawler tells WHO. "She is putting her fingerprints on it."
Kate wants to help attract younger athletes. "What keeps recurring is her interest in the cycle, the journey that the athletes and families are on. There is this massive backstory to the athletes. She is always asking, 'What is the journey?' " says Lawler. "She is keen to meet mums and dads of these athletes too."
Chatting with the royal mom in person, "she is extremely disarming, very easy to talk to," adds Lawler. "She makes them feel much more relaxed than you might think a young person would feel in that situation so they give that little bit more about hopes and fears.
"What is very evident is that she admires what they are able to do with their busy lives and school and so on. And they take from that inspiration and motivation, that she, as patron, knows a little but about them and is curious about sport. Her questions are pointed, possibly about training, competition day and nerves."
He sees the charity possibly tying in with the mental health mission that Kate and husband Prince William and Prince Harry have initiated via their Heads Together campaign. "They have a common passion in that area, and it allies with the government strategy for sport that has a direct reference to mental wellbeing."
The pre-dinner reception was held in the beautiful gardens of Kensington Palace, while the dinner was in the King's Gallery inside.
She met athletes such as Tanni-Grey Thompson and Sharron Davies as well as 18-year-old boxing hopeful Chantelle Reid.
Grey-Thompson said, "It's fantastic having the Duchess as patron.
"What's amazing about her is that at events such as the Copper Box [when she played volleyball in her wedges in October 2013] she's always the first to throw off her shoes and get stuck in as she's so fit and plays so much sport.
"She knows how important sport is and how it helps."
Chantelle Reid, from Derby, added, "I told the Duchess how much SportsAid has helped me with my funding, Physio and nutrition. "I get around £5000 a year and I really hope to make it for Tokyo 2020."
She is one of the first to receive a "Backing the Best" grant which aims to reach those from the most disadvantaged backgrounds.