But is it possible to look thinner instantly? Reality star Kelly Osbourne, 25, claimed her fake tan makes her look 10lb lighter.
To test the theory, we asked James Read, from thetantalist.com, to give it a go.
James, whose tanning clients have included everyone from Lady GaGa to Kate Moss, says: "Having a tan won't make you instantly lose weight, but it can give your body definition.
"By using tanning and layering techniques, you can achieve an instant athletic appearance.
"By contouring the correct areas like decolletage, arms and stomach muscles you can easily appear more toned."
Here James shows you how on our size 12-14 model, Dannielle Appleby, 25, from Tamworth, Staffs.
Start by applying a base colour tan in a shade of your choice. Ideally you should apply this the night before and rinse off the excess as normal.
Next you need to darken any areas you want to contour. Use a good spray tan such as L'Oreal Sublime Bronze Express Pro Self-tanning Dry Mist(£13.99, Boots).
It is designed to give the same effect as a salon spray tan and its special nozzle means there is less wastage than from your average spray-tan in a can.
ARMS: Stand in front of the mirror and do a "he-Man" - flex your muscles and pose.
Use the spray to define the muscles you already have. Lightly mist the underneath of arms and then spray more tan over the muscles to give them more definition.
Highlight any dips. This will give you the appearance of a toned, athletic look.
LEGS: Spray down either side of the legs.
By doing this you are making the legs look narrower by drawing the eye to the middle area.
STOMACH: Spray either side of the stomach, working with the natural lines of the muscles.
Add definition by darkening any areas that naturally dip in.
This will make you look slimmer by drawing the eye to the defined areas.
DECOLLETAGE: Adding a deeper colour on the collarbone using a bronzer will instantly draw the eye to the slim area.
Spraying either side of your neck will make it look slimmer and longer.
Also add bronzer to the cleavage to define the breasts.
CHEEKBONES: Spray-on foundation is big at the moment. You can spray this over your tan to give a flawless finish and then work with a bronzer over the top to define any areas on the face.
Suck your cheeks in and work bronzer underneath the cheekbones where they jut out slightly. This will make them look more pronounced.
DANIELLE'S VERDICT: "The tan did make me feel more toned and more confident.
"I went out afterwards with bare legs - which is a first for me.
"I'll definitely be trying it myself this summer."