The controversy surrounding carbohydrates, insulin, and obesity is unlikely to end anytime soon. As such, it’s worth revisiting prior issues of Study Summaries that have shed light on the topic:

The September 2020 issue of Study Summaries includes a review of a secondary analysis of another randomized controlled trial that analyzed the estimated caloric requirements of participants on either a low- or high-carb diet during a weight-maintenance period. The average estimated caloric requirements were about 245 kcal/day higher in the low-carb group than in the high-carb group. However, the interindividual variability was high, and some of the methodology used in the original trial has been hotly contested.

The December 2020 issue of Study Summaries includes a review of a 4-week crossover study comparing the effects of a plant-based low-carbohydrate diet (LCD: 10% carbs, 50% fat, 40% protein), an animal-based LCD (10% carbs, 60% fat, and 30% protein), and a low-fat diet (LFD: 61% carbs, 21% fat, and 18% protein) on body composition and blood markers. All three diets resulted in weight loss, but the plant-based LCD group lost more weight than the LFD.

The January 2021 issue of Study Summaries includes a review of a meta-analysis of 38 randomized controlled trials that investigated the effects of low-carb diets, low-fat diets, or both, on weight loss and blood lipids. Low-carb dieters lost about one additional kilogram of weight overall, and this difference was most notable when the diets ranged from 6 to 12 months. Triglycerides were reduced more by low-carb diets, whereas LDL-C, HDL-C, and total cholesterol were reduced more by low-fat diets.

The same January issue of Study Summaries includes a review of a systematic review of 8 randomized controlled trials comparing saturating fat intakes and measurements of body weight, blood glucose, cholesterol, and blood pressure among adults with a BMI of at least 25 who ate either a low-carb, high-fat diet (LCHF) or a low-fat diet (LF). Both diets resulted in significant weight reduction, improved blood glucose levels and inflammatory markers, and lowered blood pressure. The reduction in LDL cholesterol was stronger in the LF diet group, while increased HDL cholesterol and reduced triglycerides were observed in the VLCHF group.

The same January issue of Study Summaries includes a review of an 18-month study assessing the effects of a low-carbohydrate Mediterranean diet (LCMD) on hepatic fat content and visceral adipose tissue compared to a low-fat diet (LFD). The participants in the LCMD group had a greater reduction in hepatic fat content than the participants in the LFD group. After adjusting for changes in visceral adipose tissue, the LCMD group also experienced greater improvements in blood lipids, blood pressure, and cardiovascular risk score.

The March 2021 issue of Study Summaries includes a review of a crossover study in which participants followed a low-carb diet (LCD: 10% carbs, 75% fat) and a low-fat diet (LFD: 75% carbs, 10% fat) for two weeks each. The two diets led to similar weight loss (1–2 kg / 2.2–4.4 lb, over two weeks). However, the low-fat diet led to a greater reduction in fat mass, whereas the low-carb diet led to a greater reduction in fat-free mass.

The same March issue of Study Summaries includes a review of a meta-analysis of 18 randomized controlled trials that investigated the effects of a ketogenic diet compared to a low-fat control diet. The ketogenic diet reduced body weight, BMI, fat mass, fat-free mass, waist circumference and visceral fat, lean body mass, and body fat percentage, compared to a low-fat diet. Variability between studies was found for body weight, fat mass, and BMI. BMI was not reduced in studies that included only women.

The September 2021 issue of Study Summaries included a review of a meta-analysis of randomized controlled trials assessing the relative effectiveness of low-fat/high-carb (LFHC) and low-carb/high-fat (LCHF) diets on weight loss and cardiovascular risk factors. Compared to LFHC diets, LCHF diets resulted in a greater weight loss (−1.01 kg) and a greater increase in HDL-C (+7.7 mg/dL). However, LCHF diets resulted in a smaller decrease in total cholesterol and LDL-C (−24.4 and −22.8 mg/dL, respectively).

The December 2021 issue of Study Summaries includes a review of a 6-month, nonrandomized controlled trial in which participants consumed either a low-carb diet (LCD) or a low-fat diet (LFD). Compared to baseline, both diets improved triglycerides, HDL-C, diastolic blood pressure, fasting blood glucose, and waist circumference. The only significant difference between groups was for triglycerides, which showed greater reductions with the LFD.

The February 2022 issue of Study Summaries includes a review of a 6-month randomized controlled trial that randomized people with type 2 diabetes to follow a low-carb, high-protein diet (LCHP: 14% carbohydrates, 28% protein, 58% fat) or a low-fat diet (LFD: 53% carbohydrates, 17% protein, 30% fat). Body weight decreased in the LCHP group compared to the LF diet (−4.1 vs. −1.0 kg), and markers of glycemic control improved to a greater extent in the LCHP group compared to the LF diet.

The March 2022 issue of Study Summaries includes a review of a meta-analysis of 61 randomized controlled trials comparing the effects of low-carb weight-reducing (LCWR) diets with balanced-carbohydrate weight-reducing (BCWR) diets on body weight and cardiovascular risk factors among 6,925 participants with obesity. Participants without T2D experienced greater weight loss (−1.07 kg) in the low-carbohydrate diet group over 3 to 8.5 months, compared to the balanced-carbohydrate diet group. Similarly, there was greater weight loss (−0.93 kg) in the low-carbohydrate diet group over 1 to 2 years. Participants with T2D experienced greater weight loss (−1.26 kg) in the low-carbohydrate group over 3 to 6 months, compared to the balanced-carbohydrate diet group. However, at 1 to 2 years, there was no difference in weight loss between groups.

Are carbs to blame for the obesity epidemic? Original paper