- The diet must be based on an individual's preferences and metabolism
- The diet must be almost exclusively whole foods (95% or more of foods eaten)
- The diet must be an approach the individual can integrate into their long-term everyday life - it's a permanent change in how they eat
The majority of the research data we have typically compares two or more dietary approaches (example - low-fat versus low-carb) in groups of randomized participants. Sometimes researchers take these investigations to the next level and have participants "cross-over" to the comparison diet to see what happens. Both are useful in our understanding of how macronutrient mix affects weight loss, but these approaches still fail to tease out critical individual metabolic factors in weight loss.
To take such an individualized approach, researchers need to randomize participants not only into groups based on macronutrient mix, but also individual confounding factors, like whether one is insulin resistant or not. These types of studies account for what is called "confounding factors" - things that can affect outcome but sometimes are not accounted for. These types of studies are also tedious and time-consuming, but extremely valuable for the data they provide.
Dr. Caroline J. Cederquist, MD today writes about such a study in NewsBlaze, "All About You, not Low-Carb or Low-Fat." She writes about a recent study - one that slipped by my radar to write about - in which 21 obese, non-diabetic women were included to investigate high-carb versus low-carb diets. Researchers did blood tests and divided participants according to whether they were insulin sensitive or insulin resistant. The study was published in April 2005 in the journal Obesity Research.
Then they were randomly assigned to receive either a high-carb/low-fat diet, or a low- carb/high-fat diet. Both diets offered the same overall caloric content; only the macronutrient proportions were different. The HC/LF diet was 60 percent carbs, 20 percent fat and 20 percent protein, while the LC/HF diet was 40 percent carbs, 40 percent fat, and 20 percent protein.
The subjects were kept on the controlled diets for 16 weeks. They were tracked for changes in their body weight, overall insulin sensitivity, blood lipids (fats) and their resting energy expenditure, a measure of metabolism.
The results were interesting and revealing...
- The insulin-sensitive women on the high-carb diet lost about 13% of their initial body weight
- The insulin-sensitive women on the low-carb diet lost only about 7% of their initial body weight
Now that sounds pretty damning for low-carb doesn't it? But, wait...let's look at how those who were insulin resistant fared...
- The insulin-resistant women on the high-carb diet lost about 8% of their initial body weight
- The insulin-resistant women on the low-carb diet lost about 13% of their initial body weight
The differences were not explained by changes in their resting metabolic rate, activity level, or overall intake, which of course was the same for both groups. And the changes in overall insulin sensitivity during the course of the study corresponded with the degree of weight lost by the participants. Those who had been insulin resistant developed improved sensitivity.
These results were dramatic and highlight how important it is for healthcare professionals to take an individualized approach when helping patients find a dietary program to lose weight. While this was a small study, if it is confirmed by larger studies it will have major implications for how dietary recommendations are tailored for individuals.
The researchers were confident in their findings that insulin-sensitivity is a major influence in weight loss and concluded that "The state of Si [insulin sensitivity]determines the effectiveness of macronutrient composition of hypocaloric diets in obese women. For maximal benefit, the macronutrient composition of a hypocaloric diet may need to be adjusted to correspond to the state of Si."