Just to add on to what Dr McDougall has said...
I have always found the following study eye-opening in regard to this issue. And, it really challenges the whole concept of sugar and weight, and the glycemic index and weight.
The study compared two diets both containing the same amount of calories (1100)), and the same percentages of fat (11%), protein (19%) and carb (71%). The only difference was where the carbs came from. In one group, 43% of the calories came from white sugar. In the other diet, only 4% came from white sugar. Thats 118 grams (around 30 tsps) vs 11 grams (around 3 tsps)
Both groups experienced the same decreases in weight, blood pressure, percentage body fat,and the same changes in total cholesterol, LDL cholesterol, HDL cholesterol, and triglycerides. There was no difference in the effect of either diet on fasting blood sugar (which went down in both groups)
Why? Total calories were restricted and both groups lost weight. Each group took in around 1100 calories and lost about 7 kgs (almost 15 bs) over the 6 weeks.
The authors concluded...
"We therefore conclude that the use of sucrose in a weight-loss regimen is unlikely to cause problems for the average patient, as long as total energy intake is restricted."
I would not recommend a diet that has 43% of its calories coming from white sugar,
but this clearly lets anyone know that small amounts of sugar are not the problem and may help with compliance. Total calories are.
Am J Clin Nutr. 1997 Apr;65(4):908-15.Metabolic and behavioral effects of a high-sucrose diet during weight loss.
In response to evidence linking obesity and high amounts of dietary fat, the food industry has developed numerous reduced-fat and nonfat food items. These items frequently derive a relatively large percentage of their energy from sugars and the effect of these sugars on weight regulation is not well known. We studied the comparative effects of high- and low-sucrose, low-fat, hypoenergetic diets on a variety of metabolic and behavioral indexes in a 6-wk weight-loss program. Both diets contained approximately 4606 kJ energy/d with 11% of energy as fat, 19% as protein, and 71% as carbohydrate. The high-sucrose diet contained 43% of the total daily energy intake as sucrose; the low-sucrose diet contained 4% of the total daily energy intake as sucrose. Twenty women aged 40.6 +/- 8.2 y (mean +/- SD) with a body mass index (in kg/m2) of 35.93 +/- 4.8 consumed the high-sucrose diet; 22 women aged 40.3 +/- 7.3 y with a body mass index of 34.93 +/- 4.4 consumed the low-sucrose diet. Mixed-design analysis of variance showed a main effect of time (P < 0.01), with both diet groups showing decreases in weight, blood pressure, resting energy expenditure, percentage body fat, free triiodothyronine (FT3), urinary norepinephrine, and plasma lipids. Small but significant interactions were found between group and time in total cholesterol (P = 0.009) and low-density lipoprotein (LDL) (P = 0.01). Both groups showed decreases in depression, hunger, and negative mood, and increases in vigilance and positive mood with time (P < 0.01). Results showed that a high sucrose content in a hypoenergetic, low-fat diet did not adversely affect weight loss, metabolism, plasma lipids, or emotional affect.