Statistical mumbo-jumbo is not my strong point.
From the review:
Although the majority of the enrolled subjects were middle-aged and free of such chronic comorbidities as diabetes and coronary heart disease, healthcare professionals dominated in the US cohorts, who may not truly represented the average population in the community.
So, basically gathered from studies of healthy people.
However, this analysis is based on limited observational studies and large-scale trials on the complex interactions between low-carbohydrate diets and long-term outcomes are needed.
A quick look at the type of studies they used. There are 9 studies included in the review data, listed here: Table of studies. The ones without asterisks were used.
[29] 78,779 US women who were free of cardiovascular disease and diabetes in 1980 and completed a food frequency questionnaire.
[30] 82,802 women in the Nurses’ Health Study who had completed a validated food-frequency questionnaire.
[31] Associations of glycemic index and glycemic load with incident CVD were examined in a prospective cohort of 15,714 Dutch women age 49 to 70 years without diabetes or CVD. Dietary glycemic index and glycemic load were calculated using the glycemic index, carbohydrate content, and frequency of intake of individual foods.
[11] 42,237 women, 30-49 years old at baseline, volunteers from a random sample, who completed an extensive questionnaire and were traced through linkages to national registries until 2003.
[12] Participants were 22 944 healthy adults, whose diet was assessed through a validated questionnaire. Participants were distributed by increasing deciles according to protein intake or carbohydrate intake, as well as by an additive score generated by increasing decile intake of protein and decreasing decile intake of carbohydrates.
[7] Limitations - Diet and lifestyle characteristics were assessed with some degree of error, however, sensitivity analyses indicated that results were not unlikely to be substantially affected by residual or confounding or an unmeasured confounder.
[8] Dietary habits were determined by 7-d dietary records in a population-based longitudinal study of 924 Swedish men (age: 71 ± 1 y).
[9] Women aged 30-49 years, residing in the Uppsala healthcare region in Sweden in 1991-92, were the source population for the Swedish Women’s Lifestyle and Health Cohort. For this cohort, 96 000 women were randomly selected from four age strata (30-34, 35-39, 40-44, and 45-49), invited by mail to participate, and asked to fill in a questionnaire and return it in a pre-paid envelope.
[10] Median intakes of carbohydrates, protein and fat in subjects with LCHP scores 2-20 ranged from 61.0% to 38.6%, 11.3% to 19.2% and 26.6% to 41.5% of total energy intake.