Is eating straight sugar ok, as long as I eat it with fiber?

In whole fruits, sugar is "embedded" in the fruit, not necessary chemically, but physically. It takes some time for the digestive system to extract sugar from the fruit, which slows down its absorption.

If you eat a whole mango, all the sugar from it will be absorbed, let's say in 2 hours. If you make a thick juice from mango, both fiber and sugar will be present in it, but will be separated, so your digestive system will be able to extract free sugar from it faster than from a whole fruit, let's say in an hour and half. The presence of fiber will still slow down the absorption of sugar a bit, but not as effectively as in whole fruit. This also applies for the cola + fiber example. This means that blood glucose spikes will be likely higher after drinking fruit juice than after eating whole fruits.

They are 2 main reasons why free sugar can be more harmful for health than the sugar from whole fruits:

• It is less filling, so it's easier to consume it too much, which can result in an unwanted weight gain
• It more likely results in higher blood glucose spikes (higher glycemic index) than the sugar from whole foods, which may be a risk factor for diabetes type 2.

Sources:

• Fruit juice (Defeatdiabetes.org): a simple explanation with references to studies
• Fruit consumption and risk of type 2 diabetes: results from three prospective longitudinal cohort studies (BMJ, 2013)