Hi
Your comments has lots of parts; trying my best to keep it balanced, concise and jargon are kept to a minimal

Q1: I read that juice loses it's nutrients the moment it's squeezed fresh, even more so after it's been pasteurized and packed till most the vitamins are gone.

Yup you are right! Taking a common “juiced” fruit - orange as an example. The percentage of vitamin C (a common form of ascorbic acid) in orange pulp is relatively higher than that of its freshly squeezed juice.

A major contributing factor for this lies in the component called citrus flavonoids. Citrus flavonoids which have been linked to being anti-oxidants and anti-mutagenics (ability to prevent cells from mutation) exist in abundance in the fruit's pulp, and skin. (yea I know we dun “juiced” the skin)

Heat (through pasteurization or otherwise) will certainly reduce the nutritional content of juice.

For example, vitamin C reacts readily with oxygen, gets broken down at about 70degress or more and is also a water soluble vitamin. Hence, an exposed jug of freshly squeezed juice or a cut fruit are not your best friend when it comes to conserving vitamin C.

Of course, orange is more than just vitamin C. It is also a great source for Thiamine (vitamin B1) and dietary fibre. And each of these will react differently when exposed to variables.

Q2: thing is, the vitamins printed on juice packs look promising.

Hmm… actually I seldom find these values promising …. Most are packed with high sugar % or tend to be syrup based mix.

Sidetrack: No sugar added doesn’t mean no sugar in the drink. These could be due to the fact that the ingredients already contain high sugar content.

For guide to Recommended Dietary Allowances RDA by Singapore HPB, you can visit: http://www.hpb.gov.sg/foodforhealth/article.aspx?id=2652

Q3: do they actually measure the amount of vitamins on the fruits before they squeeze em; pasteurize and pack em OR do they measure the nutritional value after all the processing before they are packaged?

As the manufacturers have a responsibility to uphold the stated the nutritional value, and sampling(testing) of the product is based on the principle of “at the point closest to the consumer”, think we have sufficient reason to believe the values listed are as close to the final product (though it may not imply that it is the final product) that we drink or eat.

You can refer to Section C – Nutrients Claims Verifications of the HPB guidelines for details. http://www.hpb.gov.sg/edumaterials/download.aspx?id=988

Btw, I am not from HPB

Q4: if i is the latter then why do we even drink juice anyway? Refreshment, sugar rush, satisfaction etc…. 101 reasons to drink (liquor) too 

Q5: Also, if nutrients are lost when we cook food, does a soup/ stew that has been left simmering for hours lose almost all the nutrients? Would most of the nutrients in the meat and greens be absorbed by the liquid of the soup/ stew?

Yes to the first part. Since we know exposure to high heat/prolonged heat/air/water etc would break down/lose the nutrients. However, the amount of nutrients that you can derive depends on your cooking method.

Assuming that the pot was covered by a lid, this would imply that the amount of nutrient retained would still be higher than if an uncovered pot was used. And you would still be able to derive the nutrients from the constituents provided you drink all of the stew/soup…. (…certainly you dun want to do 30mins before a Muay Thai training….)

Sidetrack: Note that these don’t mean that we should just turn into “raw eaters”.

Cooking can also help to increase the nutrient’s bioavailability (quantity of the nutrient that can be digested and absorbed), For instance, steaming carrots helps to break down their sturdy cell walls, thus facilitating the release of Beta-Carotene. Also, we can derive the minerals from bones via cooking them in soup.

Interesting....

wahh! great reply man, you sound like a pro hehe thx for the info, looks like we should eat more fruits and drink less packaged juice

thanks part of our value added services is also to advise our personal training clients on their health/nutrition req'd.

Feel free to pm us or post QnA in MT.sg; will address them to the best of our knowledge