How did they come to the 6 and 9 teaspoons of sugar limit figures?

At 57:40 minute of the video Dr Lustig proudly presents his part he played in the project for reduction of daily sugar intake down to 6 teaspoons for women and 9 teaspoons for men. 

I have no problem with reducing sugar intake by anyone. I have done it myself. Aside from that many nutrition professionals consider this amount as unrealistic in this current sugar loaded society and market, it was interesting to find out the story behind these new limits of sugar consumption. I found it just by chance and I believe that you will find it as interesting as I did. I admit I previously read the paper when I did my own research but I did not think hard about how they came to the figures because my focus was on the evidence of the negative health impact of fructose consumption. I have realized this interesting background only recently when I heard it discussed by Alan Aragon, who also questioned the fructose story of Dr Lustig back in 2012. Have a look at 31 minute of this video, the explanation only lasts 5 minutes. 

It came out that these amounts of sugar, corresponding to 100 kcal for women (6 teaspoons) and 150 kcal for men (9 teaspoons) were just made up as half of the discretionary calories recommended by the U.S. government. These discretionary calories were set up as 10% of total energy intake, because it was understood that people were likely to cover their nutritional needs when nutritious food contributed with 90% to their total daily energy requirements. Hence they could expand on the hedonistic experience by consuming other food items, such as sweets, butter or alcohol, which made up no more than those 10% to fit into the balanced energy intake, i.e. not gaining or losing weight when eating this way. The team, including Dr Lustig, just halved these 10% into 5% and allowed people to consume this amount of calories in a form of sugar. Mr. Aragon hypothesized that the scientists assumed that the remaining calories will be filled with solid fat intake or also the alcohol. The AHA Scientific Statement (the one in the slide) says that when people consume alcohol, their added sugar and solid fat intake should be even lower to maintain those 10% of discretionary calories overall. Exercising people can consume more, of course, but this was not mentioned in the lecture and on the slide above. 

One thing should be noted: nobody can follow this guideline to the point on daily basis. The figures represent average value and should be met within overall daily consumption over several days as mean value. 

Now you might have realized that from percentages we have suddenly moved to the absolute amounts - the same amounts for every woman or man, regardless of their actual energy needs or expenditure. at least according to the slide mentioned earlier. 

However, the AHA Scientific Statement itself, albeit just briefly, included more information: 

Now I am asking: who is the average adult woman or adult man? 

They do not exist, it is just a reference point to give an approximate idea about the amounts. 

You have probably noticed that the figures in the Statement were slightly lower than those presented in the slide. This is because the figures on which the team made the recommendations refer to the past, when people had a lower body mass on average. You might already know that today we are heavier than our parents were, because we also eat more calories (or rather move less). The average woman energy intake today is 2000 kcal and for an average man it is 2500 kcal. You can find these figures on almost every processed food package, close to the Nutrition Facts table. Those old figures referred to an average woman, weighing about 60 kg, and it included young women as well as elderly. Those 60 kg is no longer real though. 

As I said previously, I do not object against the recommendations to eat less sugar. It was the method of coming to the specific numbers that amazed me. And the Statement also admitted that these numbers are not realistic: 

It seems that if you consumed more than the prescribed amount of teaspoons of sugar, your health would be affected badly, regardless of whether you drunk alcohol and/or ate the solid fat or not. Do you understand what I mean? They expect that everybody has the same diet as any other person and that everyone consumes half of their discretionary calories as sugar and half as solid fat. What if some people consume less solid fat? Will Dr Lustig tell them off for exceeding the new allowance for sugar, because they drunk one can of soda?

Finally, I have found the following piece of information, cropped from the slide presented at 59:53 minute, intriguing: 

Three points I would like to make here: 

1. These new amounts (limit of 9 and 6 teaspoons of sugar per day) were therefore not based on any study for a safe threshold of sugar consumption. The figures were just made up. Dr Lustig & co. basically created these amounts and he judges the general population about the amounts of sugar they are consuming today in respect to the newly created allowance limit; exercising or not, obese or not, guilty as charged. 
2. These new limits still reflect the relative body size and muscle mass of two sexes (men and women). But they do not correspond to the actual size and capacity of their livers to metabolize the fructose. From these new thresholds it still appears like if men could safely handle 30% more fructose than women, which does not have a support in the science.
3. In addition, what this basically means is that this argument still focuses on body weight, not on the metabolic health, especially of the liver. Although the Statement was published in 2009, Dr Lustig brought it to your attention again relatively recently; the video was published in March 2014. Therefore this is another discrepancy of the aims and efforts proposed by Dr Lustig. The obesity is not a problem anymore - he now says, it is the health of the liver. However, the metabolic risk for the liver was left out when using this argument. 

And that is it. You now know how some public health figures are made up. There was actually more I would like to comment on that paper. In the following article you will learn how some of such respected papers still can misreport the information which they refer to.