"Possibly the hardest thing as a girl growing up was accepting body image – being quite muscly was not the norm in my peer group and I agonised over it," she tells The Huffington Post UK.
Ennis-Hill, who is shortlisted for Sportswoman of the Year this week, now feels "really happy with how I look" and says she has "an amazing career in a sport that has equality".
But as she and the five other shortlisted athletes explain, there are still challenges for women in sport - they receive far less recognition, media coverage and sponsorship than their male peers.
Ennis-Hill after winning the heptathlon 800m at the 2015 World Athletics Championships in Beijing
HuffPost UK spoke to the six women shortlisted for the prestigious Sportswomen of the Year Awards on 6 November, and asked them what they consider the best and worst thing about being a woman in sport.
Rachel Atherton, the two-times British mountain biking champion, says that in her sport that is "still dominated by men... some of the younger girls do still feel pressured into photo-shoots that focus on how sexy they look."
World champion track and road racing cyclist Lizzie Armitstead admits she doesn't get "as many opportunities to race" as men in her position.
There are also few female role models on the management side of sport, "particularly if you look at coaches and technical experts," says Lizzy Yarnold, who won gold for Britain in the skeleton at the last winter Olympics. "It’s hard to see where your career could progress after you have finished," she added.
But as the media and public pay more attention to Britain's female athletes and more role models become visible, the situation is changing for the better.
"The best thing about being a women in sport is being able to show girls and women of all ages the confidence and strength that sport can give you," says Atherton. "I know that I feel like a better person after I have ridden my bike."
All six athletes are shortlisted for the 2015 Sunday Times and Sky Sports Sportswomen of the Year Awards in association with Vitality, celebrating women in sport at all levels. Watch on Sky Sports 1 and Sky 1 on 6 November.