People reaching for a protein bar, thinking it's a healthy snack, may be unwittingly adding to their waist lines.
The NZ Nutrition Foundation has expressed concern about adults and children using food designed for elite athletes - such as protein bars, supplements and energy-dense sports drinks.
Chief executive Sue Pollard described the bars as "totally unnecessary and certainly not recommended for the general population".
The Herald on Sunday compared a selection of supermarket-brand protein bars to a handful of chocolate bars.
It showed that the 100g Aussie Bodies HPLC Bar packed more kilojoules than Mars, Snickers, Twix or Bounty bars.
Another, Protein 33, was only just less kilojoule-dense.
With 17.9g of sugar, Protein 33 had two-thirds of the sugar of a Snickers or Twix bar, and half as much as a Mars bar.
Carb Less Deluxe and Atkins bars had less protein than a small can of tuna and only slightly more than a glass of milk.
But they are a lot more expensive - the cheapest bar we bought was $2.99 and the most expensive $5.39.
Healthy Food Guide nutritionist Claire Turnbull said people had a misconception that a protein bar was a guilt-free, everyday snack option.
"They vary hugely, from tiny ones to some that have far more energy than a chocolate bar."
She said some contained ingredients such as sorbitol and sugar alcohols that aggravated conditions such as irritable bowel syndrome, and had "millions" of ingredients.
She said people who wanted to eat healthier would be better to have snacks such as tuna or a boiled egg.
"The other thing is that they're really sweet so it doesn't teach you not to like sweet food.
"I think you're better to reduce your taste for sweet food. Protein bars are okay occasionally, if that's what you want, but people need to be aware of what they're buying."
Former Mr International, Australia, James Mathieson, said he used protein shakes and bars carefully for muscle building, before and after a workout.
"To get optimum results, I have a workout, then a half-hour sauna, then a 20-minute shower, then have a protein bar within an hour. You can see the results happen."
He said he would have no more than two bars a day and would not mix bars and powder. "That amount of protein pumped into you - you don't need it."
AUT senior lecturer and Nutrition Foundation dietitian Caryn Zinn said supplements were necessary only for people who were going to be exercising at reasonably high intensity for more than an hour.
People running a marathon would benefit from a sports drink and protein boost but kids heading out for a game of cricket would not.
She said sports drinks were ostensibly marketed to sportspeople but, in reality, were designed to appeal to everyone, particularly children, with a range of colours and flavours.
Calorie-free sportsdrinks were a better alternative for the general population, but pointless for athletes, she said, "For athletes, if they need fluid and electrolytes in exercise sessions lasting longer than 1.5 hours, carbohydrate is necessary."
She said people who added a protein shake to their regular diet without exercising more or adjusting the rest of what they ate would put on weight.
"I would caution against using them inappropriately."