I haven't read the whole draft report but I did scan thru is and apparently they did look at randomized controlled trials (the gold standard) but, "in the absence of RCTs" ALSO resorted to relying on other types of studies, such as "prospective studies" (which I take to mean epidemiological crap.
Most weight is placed on evidence from randomised controlled trials (RCTs) since well-conducted RCTs minimise the potential for selection bias and confounding. Less weight is placed on observational studies because such studies are potentially subject to bias, confounding and reverse causality. However, in the absence of RCTs, evidence from non-randomised intervention studies and prospective studies is considered stronger evidence than other study designs...."
Tho they were willing to resort to epidemiology, they specifically EXCLUDED reports from practicing physicians such as Dr. Unwin. In fact, studies by both Hallberg and Unwin are mentioned by name as not meeting their "inclusion criteria."
A number of clinical studies (including Saslow et al (2017); Bhanpuri et al (2018); Hallberg et al (2018), Athinarayanan et al (2019)) and case reviews (Unwin & Tobin, 2015) have assessed the effectiveness of lower carbohydrate diets on glycaemic control and other markers in adults with T2D. These are largely based in primary or secondary care clinic settings or use data from participants self-enrolled in commercial dietary programmes. The study design employed in such published research includes quasi-experimental studies, nonrandomised trials, single-arm trials or experiences in clinical practice. Some of the key limitations of these studies are: lack of randomisation, lack of a comparator arm and self-selection (for example, participants may choose a particular study or study arm).
These studies were not considered in this report because of the number of limitations associated with this study type. They also did not meet the inclusion criteria for study selection
Finally, although I haven't read the report carefully, I can't find any mention of what constituted an acceptable "lower carbohydrate" diet plan for inclusion within this study. I strongly suspect that most, if not all, of the included RCT studies were probably had their "lower carbohydrate" arm eating 45-50% carb diets and comparing that against a control group eating 60% or more carbs.
Pretty much everyone with any real experience with low-carb dieting agrees that 50% carbs is NOT low-carb enough to be of benefit. And those of us with experience with controlling T2 diabetes with diet KNOWS that you have to go a whole lot lower than that. (My husband has been successfully controlling his T2 diabetes now for over five years with diet alone!)
Having SEEN firsthand the benefits of T2 patients going low-carb, no clinician worth his/her medical license is going to recommend that ANY patients enroll in a study where there is a 50% chance that they're going to be told to eat a high carb diet! Can you imagine Dr. Unwin being willing to send one of his patients to such a study???
So, the necessary studies to meet the "inclusion criteria" for reports like this SACN report are probably never going to get done. Instead, hopefully, more and more real doctors will learn from one-other... or from their patients... that low-carb WORKS. Eventually, low-carb will become the defacto acceptable treatment for T2 diabetics. It's just too bad that, in this instance, the scientific method is slowing down the progress of truth being spread.