Posted by: Bea | 2004/11/06

Negative calories and kelp

Hi DietDoc!

I've got 2 questions:
1) Do you think there's ANY truth in the 'negative calorie' theory?
Some people claim that certain foods, such as apples, carrots, cabbage, tomatoes, cucumber etc are so rough that the body uses more energy in breaking them up than they contain in themselves, say an apple that contains 65 C, would require 70 Calories to be broken down, so in effect there's a shortage of 5Calories. i.e. -5 C.
Does this phenomenon exists?

2) Secondly, I would like to have your opinion on the eating of Kelp to speed up one's metabolism. Myth or Fact?
And would I have to eat raw kelp, those slimy bitter plants one gets in the ocean?? or should I rather go for the tablets one can buy in shops? (at least they're not that bitter)
Or would it just be a waste of time, money and taste buds and stomach space?

Thank you so much for your informative and logical replies to all the questions in this forum.


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Our expert says:
Expert ImageDietDoc

Dear Bea
Here are the answers:
a) The negative energy theory is perfectly correct. Certain foods (also called 'free foods" e.g. tomatoes, watercress, lettuce, cucumber, gherkins, etc) have such a low energy content that it actually takes more energy to digest them, than they contain. This does, however, not mean that you can exist exclusively on these foods when you are trying to lose weight. You still need to include other healthy foods such as other fruits and vegetables, lean meat, fish, eggs, wholegrain cereals, fat-free milk and dairy products, and even small quantities of poly- or monounsaturated margarine and/or oil. You can certainly use these very-low-energy (because they contain so much water) to lend variety to your diet and to fill you up.
b) The reason why these kelp products may increase your metabolism is because they contain iodine which is required for the normal function of the thyroid gland. However, all the table salt sold in SA has been fortified with iodine for quite a long time, so the population should no longer have an iodine deficiency. You can also eat fish 3 times a week for its iodine content and other benefits, like the omega-3 content, without having to eat seaweed or take those tablets.
Best regards

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