Pippa Middleton diet & fitness secrets: Kate Middleton's sister shows washboard abs during vacation at St. Barts

Kate Middleton's sister, Pippa Middleton, is looking extremely fit and sexy while vacationing in the isle of St. Barts with her mom and brother. In a red bikini, she has shown her flat, washboard abs and toned physique, making everyone wonder how she has done it or what is her diet and fitness secret.

Celebrity Health & Fitness shares that Pippa has been a long-time fan of fitness and exercise, that is why she has always looked ripped and slender. Pippa has been reported to have joined and competed in marathons, triathlons, and this coming September, the Duchess of Cambridge's sister will be competing in the Otillo Swim-Run World Championship, a 47-mile race to be held in Sweden.

Besides being naturally athletic, Pippa credits her fit body to healthy diet and exercising for three to five days in a week, which Pilates and running are a part of. She doesn't have faith in extreme diet changes nor too much workout because she states that moderation is the key to her fitness success.

US Weekly writes that Pippa has grown up in a household that believes in taking everything in moderation. This is the reason why she follows a healthy living lifestyle by incorporating a balanced diet, enough exercise and once in a while, adding chocolates and the occasional red wine to break the monotonous pattern.

For her fitness regimen, she follows mainly simple moves like ladders, plié squats, planks and wall pushes while doing a two-minute rest in between circuit training. It is her best moves yet for completely toning the body. Furthermore, Pippa shares that staying active and making it a habit to try sports keep her mental health and well-being well-rounded.

Last year, The Examiner has reported that Pippa has denied following fad diets like the Dukan and Atkins because she feels making health choices like minimizing her refined carbs and keeping the portion sizes sensible are good enough for her. The rumors have started when Pippa and Kate's mother, Carol, has been reported to have lost weight due to the Dukan diet.

Pippa insists that in eating, she doesn't believe in depriving herself of delicious meals because she can always have them if she keeps it to a certain amount.