I'm having trouble figuring out the exact calories for a certain food I have — what's the best and most accurate source of nutrition information?

The nutrition facts vary because with many foods, there is no exact amounts. Two different food items may vary by as much as 20% of the calories. When companies produce their nutrition facts, not only are they allowed a 20% margin for error, but they are allowed to round the calories up or down to the nearest 50 or 10 increment depending on the serving size. This is why different products might have very different amounts ... because they vary.

Nutrition and tracking is useful, it creates a baseline, and forces us to be consistent with portion sizes. However, splitting the hairs doesn't serve any purpose and thinking you really get some exact number of carbs is simply not true. Pick A measurement and use it consistently. If it is the wrong one, it will come out in the wash because you'll notice if you are either gaining or losing and can adjust the portion sizes accordingly, regardless if the calorie information is exactly correct.

This is why I am mildly amused when people tell me, "My vitamin intake of this is low ... because I track it in xxxx" or "I get plenty of this ..." the bottom line is those are subject to wild error. Heck, one batch of broccoli may differ from another in Vitamin C content by hundreds of percent ... there is just no sure way of knowing. What's more, there are only a few vitamins and minerals companies are required to analyze and report, the rest they can leave off the label. For example, while sodium is required, knowing your sodium-potassium ratio is important but companies don't have to report potassium, so you almost always are taking in more than you think!