Added sugar is chemically identical to natural sugars of the same variety. The only difference is that there is more of it. It's not really the greatest thing natural or added.
The AHA recommends a maximum added-sugar intake of 25 g/day (6 teaspoons/day) for women, and 39 g/day (9 teaspoons/day) for men. Similarly, the WHO recommends that no more than 10% of total calories ("ideally less than 5%") should come from added sugar, which works out to 25 grams for a 2000-kcal diet. For comparison, the average American consumes roughly 70 grams of added sugar per day. [1]
I can't find a specific source for a ceiling of 5 g/day, but it's pretty uncontroversial that more added sugar is never better. The lower you set your maximum intake, the harder it is to maintain, since sugar is added to so many foods.
5 g/day is a somewhat arbitrary cutoff that's lower than official recommended maximums, but this doesn't imply that there should be no limit. Pick one. Or start with "as little sugar as practical," log how much sugar you end up consuming under this plan (using a food diary, food scale, etc.), and adjust as needed.
My comment above explicitly describes what I refer to as "official recommended maximums": the maximum daily intakes recommended by the AHA and WHO (among others around the globe), presumably through an audit by domain experts of the totality of epidemiological and clinical evidence, together with an unknown amount of interference from non-scientific interests.
To address your analogy, researchers are in a sense writing the Missing Manual for Humans, as our species didn't come with one.
You're free to accept or refute these recommendations, but I personally am inclined to put at least some trust into their collective efforts. Or if you trust different recommendations more so than these, I'd love to see them.
The WHO is a 71-year-old UN agency whose constitution has been signed by 61 countries. One of the organizations it incorporated was the Office International d'Hygiène Publique (https://en.wikipedia.org/wiki/Office_International_d%27Hygi%...), an international public-health organization.
I have to say I find your pushback at the term "official" perplexing. Why do you disagree with this descriptor? They're literally official. It doesn't get more official than this. Sure, they're sometimes wrong, as your fat-free reference suggests, but that's beside the point.
Yeah, and a weird pre-condition. "Have all the sugar you want, as long as it's from fruit juice"? I don't even think the high-carb low fat advocates would go along with that. That's insane.
The fact is, there is no peer reviewed research proving that eating 5g per day, or 6g or 7g or 9g or 2g for that matter will have any material impact on health.
It’s an arbitrarily chosen number. Just like most thinking around food and diet, these things are highly influenced by current trends.
Obsessing over arbitrarily specific numbers in your diet is missing the point. Just make a conscious effort to consume sugar in moderation and you’ll be fine.
The number is useful because it gives a target. Consume in moderation is a joke because moderation means different things to different people. Of course it's OK to go over or under the 5g number. That's not the point.
If obsessing over specific numbers is missing the point, then so is reporting official-sounding over-precise figures about a "recommended limit".
Sugar is bad for you? Fine. Any given unit of sugar will have worse outcomes than the absence of that sugar? Fair enough.
"Hey, we're reporting 5g as some special, significant threshold that suggests we have actual evidence of things really ramping up at that point that suggests no subjective gain could outweigh the damage to your health, when, in reality, it was just pulled out of thin air"? No. Forget that noise.
Because of the fiber in fruits and vegetables, your body digests them more slowly. Thus, the sugar enters your bloodstream more slowly.
It's kind of like the difference between drinking a beer on a full stomach versus an empty stomach.
In this case, 25g of sugar entering your bloodstream quickly is quite unhealthy.
(Related: If you want to understand this better, stop consuming refined sugar for about a month. Then go eat a peep on an empty stomach. You'll feel an intense sugar rush.)
> Most nutritionists agree you shouldn't have more than 5g of sugar outside of fruit sources-
So nutritionists do or don’t agree that it should also include vegetable sources?
Related: I’m T1 diabetic and my partner had to call 911 last week because of hypoglycemia. If I hadn’t consumed 25g of sugar quickly the result would’ve been quite unhealthy.
Starchy vegetables like potato, corn, and peas are nutritionally distinct from non-starchy veggies. But their sugar is packaged with vegetable fibre, which results in slower absorption than if you drank the same amount of sugar in liquid form on an empty stomach.
It feels a bit redundant to point out to a T1D that fruits are far higher in sugar than non-starchy veggies, which is why OP specifically mentioned fruit sources of sugar.