Here are some reasons why people might be better off eating less carbohydrates & more fat or protein:

*http://www.ncbi.nlm.nih.gov/pubmed/15148063

Compared with a low-fat diet, a low-carbohydrate diet program had better participant retention and greater weight loss. During active weight loss, serum triglyceride levels decreased more and high-density lipoprotein cholesterol level increased more with the low-carbohydrate diet than with the low-fat diet.

In addition, the low-carbohydrate group lost less lean body mass:

Patients in both groups lost substantially more fat mass (change, -9.4 kg with the low-carbohydrate diet vs. -4.8 kg with the low-fat diet) than fat-free mass (change, -3.3 kg vs. -2.4 kg, respectively).

*http://www.ncbi.nlm.nih.gov/pubmed/18635428

Mediterranean and low-carbohydrate diets may be effective alternatives to low-fat diets. The more favorable effects on lipids (with the low-carbohydrate diet) and on glycemic control (with the Mediterranean diet) suggest that personal preferences and metabolic considerations might inform individualized tailoring of dietary interventions.

The patients on the low-carb diet lost more weight & better improved HDL:

The mean weight loss was 2.9 kg for the low-fat group, 4.4 kg for the Mediterranean-diet group, and 4.7 kg for the low-carbohydrate group (P<0.001 for the interaction between diet group and time); among the 272 participants who completed the intervention, the mean weight losses were 3.3 kg, 4.6 kg, and 5.5 kg, respectively. The relative reduction in the ratio of total cholesterol to high-density lipoprotein cholesterol was 20% in the low-carbohydrate group and 12% in the low-fat group (P=0.01).

*http://www.ncbi.nlm.nih.gov/pubmed/20679559

CONCLUSION: Successful weight loss can be achieved with either a low-fat or low-carbohydrate diet when coupled with behavioral treatment. A low-carbohydrate diet is associated with favorable changes in cardiovascular disease risk factors at 2 years.

They also saw greater improvement in HDL ("good") cholesterol in the low-carb group:

Increases in HDL cholesterol levels were significantly greater in the low-carbohydrate than in the low-fat group at 3, 6, 12 and 24 months.

They also mention another reason that LDL increases in the low-carb group may not increase cardiovascular risk:

[...]assessment of LDL cholesterol concentration without information on LDL particle size has limitations as an indicator of coronary heart disease risk because small, dense LDL particles are more atherogenic than large LDL particles (24). Data from carefully controlled studies demonstrated that isocaloric replacement of dietary carbohydrate with fat increases plasma LDL cholesterol concentration but shifts LDL particle size from smaller to larger and less atherogenic LDL (25).

*http://www.ncbi.nlm.nih.gov/pubmed/12761365

CONCLUSIONS: The low-carbohydrate diet produced a greater weight loss (absolute difference, approximately 4 percent) than did the conventional diet for the first six months, but the differences were not significant at one year. The low-carbohydrate diet was associated with a greater improvement in some risk factors for coronary heart disease.

Again, the low-carb diet better increased HDL: +18.2 for the low-carb group, +3.1 for the conventional group (P=0.04).

It also better decreased Triglycerides: -28.1 for the low-carb group, +1.4 for the conventional group (P=0.04).

Note: This is a copy of a comment I posted months ago in another diet thread.