A few days ago I posted a more recent study by Chris Gardner comparing various popular diets. It was a big study and done very well, but it was based strictly on self reporting. Ideally all the subjects should live in a metabolic ward and be monitored 24 hours a day and fed exactly the right amount. But as you can imagine, that would be extremely expensive. A more affordable way to check for low-carb diet adherence can be found in your toilet.
When someone goes on a very low carb diet, their liver produces something called ketone bodies which can provide energy in place of the depleted glucose source from your diet. Ketones can be detected in the urine (called ketonuria) and therefore provide a reliable way to ensure that someone is following a low carbohydrate diet.
In a study published in Nutrition and Metabolism in 2004, researchers compared an energy restricted low carbohydrate diet to an energy restricted low fat diet monitoring ketonuria every day to make sure the low carb dieters were not cheating. The low carb diet was supposed to eat less than 10% of their diet from carbohydrates and the low fat diet was supposed to follow the national recommendations (%carb:fat:protein = 60:25:15).
Since there is a lot of variation in response to diet, the researchers also decided to compare each persons response to both diets. This is called a crossover trial. This approach allows them to compare the diets in 2 ways: between groups, and within each group between the individuals of that group. They then did further analysis to see if the order of each diet mattered.
Each group was given a detailed list of what foods they could eat and ordered to keep a food diary, and their urine was tested each day for ketonuria.
The men followed the diet for 50 days and women for 30. Between groups, men lost more weight and fat. Within groups when each individual was in their low carb phase of the diet, both men and women lost more weight and fat as well when compared to the low fat phase. All this despite the low carb group eating reportedly more calories!! (1855/day vs 1562/day in the low fat group).
Despite this being a short term study involving only about 30 people, i think it provides powerful support for the efficacy of a low carb diet for weight and fat loss. The researchers took every precaution possible to make sure that the low carbohydrate group stuck to their diet. The fact that they reported eating more calories per day is also astounding. One can claim the low carb group inaccurately reported their calorie consumption. But without any evidence that this is true, you cannot assume that their reporting was any less accurate than the low fat group.
These results also beg the question: is a calorie actually just a calorie? Most nutritionists will tell you a calorie is a calorie and you cannot disobey the 1st law of thermodynamics, but this study (along with many others to come in the future) beg to differ.