His entire theory is based on a cursory glance at a few biochemistry textbooks (and misinterpretations of basic concepts) and rodent research.
"The use of deuterated water has overcome this problem. In an elegant experiment designed to assess the relative contributions of hepatic vs. adipose DNL to adipose fatty acids, Diraison and collegues (2003) gave subjects both [1,2-13C2]acetate, which is efficiently taken up in the liver but not adipose, and 2H2O, which will equilibrate rapidly with the entire body water pool. By subtracting liver DNL from measured adipose DNL they estimated true adipose DNL, which (as with hepatic DNL) was quantitatively insignificant in humans, even under conditions of carbohydrate excess (Diraison et al., 2003). Another study (Strawford et al., 2004) investigated DNL, from any source–liver or adipose, in adipose tissue in humans using 2H2O. The advantage of this study was that the labeling was over the course of many weeks under normal living conditions, which should allow for the evaluation of DNL under usual ad libitum dietary conditions. Although absolute values for DNL were not presented, one can estimate that at most, whole body DNL accounted for 1 g/d of fatty acid synthesis. "
"In contrast with humans, DNL appears to be very active and quantitatively significant in other animals. In rodents, DNL in adipose and liver can account for over 50% of fatty acids (Lee et al., 1994a; Brunengraber et al., 2003)."
From this review.
The reason it's the alternative hypothesis is because it's not supported by any established scientific research. Carbohydrates are not inherently more fattening than fat. The insulin hypothesis of obesity is not true.