First things first - the objective of the study was to compare the effectiveness and safety of weight loss diets over a two year period.
The dietary approaches included in the study:
- a low-carb diet, loosely based upon the Atkins diet, no calorie restriction
- a Mediterranean diet, calorie restricted, based on the recommendations of Dr. Willett & Dr. Skerrett (Eat, Drink & Be Healthy)
- a low-fat diet, calorie restricted, based on the American Heart Association guidelines
In addition to weighing participants each month and measuring waist circumference, the researchers measured at reporting invervals (6-months, 12-months and 24-months) total cholesterol, LDL, HDL, triglycerides, fasting blood glucose, fasting insulin, HbA1C, blood pressure, HOMA-IR, C-reactive protein, leptin, adiponectin, bilirubin, alkaline phosphatase, alanine aminotransferase and urinary ketones.
Enrolled in the study were 322 volunteers; they were provided their largest meal each day (lunch) at work, and given support and guideance about their diet throughout the study period. Of the 322 who started the trial, 95.4% completed one year, and 84.6% (272 participants) completed the 24-months - making this perhaps, the best adherence level in a dietary trial lasting two years!
So what happened? Let's look at the various outcome measures to see.
The mean weight changes among the 272 participants who completed 24 months of intervention were:
–3.3 ±4.1 kg in the low-fat group (7.3-pounds)
–4.6 ±6.0 kg in the Mediterranean-diet group (10.1-pounds)
–5.5 ±7.0 kg in the low-carbohydrate group (12.1-pounds)
Overall, in the intent to treat data (which includes even those subjects that did not complete the study) the weight loss was reported as:
–2.9 ±4.2 kg for the low-fat group (6.4-pounds)
–4.4 ±6.0 kg for the Mediterranean-diet group (9.7-pounds)
–4.7 ±6.5 kg for the low-carbohydrate group (10.3-pounds)
The reason I note the two findings is that in the media reports, the trend appears they're reporting the intent-to-treat numbers, which are lower because they include the 50 subjects that dropped out. Those who actually completed the study are the data I prefer to look at for weight loss since it accurately presents how effective the dietary approaches are when continued for two years!
-2.8 ±4.3 cm in the low-fat group
-3.5 ±5.1 cm in the Mediterranean-diet group
-3.8 ±5.2 cm in the low-carbohydrate group
The graph itself speaks volumes:
High-Sensitivity C-Reactive Protein, High-Molecular-Weight Adiponectin, and Leptin
The level of high-sensitivity C-reactive protein decreased significantly only in the Mediterranean-diet group (21%) and the low-carbohydrate group (29%), during both the weight-loss and the maintenance phases, with no significant differences among the groups in the amount of decrease.
During both the weight-loss and the maintenance phases, the level of high-molecular-weight adiponectin increased significantly in all diet groups, with no significant differences among the groups in the amount of increase.
Circulating leptin, which reflects body-fat mass, decreased significantly in all diet groups, with no significant differences among the groups in the amount of decrease; the decrease in leptin paralleled the decrease in body weight during the two phases.
Fasting Plasma Glucose, HOMA-IR, and Glycated Hemoglobin
Among the 36 participants with diabetes, only those in the Mediterranean-diet group had a decrease in fasting plasma glucose levels (32.8 mg per deciliter); this change was significantly different from the increase in plasma glucose levels among participants with diabetes in the low-fat group.
This is critically important to note - the low-fat group experienced a rise in fasting blood glucose over the course of the two years; this despite a greater calorie deficit than the other two diets, and a greater increase in physical activity! Yet, this type of diet is exactly how the ADA recommends people at risk for or diagnosed with diabetes eat, while expecting ever increasing doses of medication to cover their progressive decline in glycemic control.
It is also noteworthy that, "there was no significant change in plasma glucose level among the participants without diabetes." Basically those who did not have diabetes did not experience any change in their values over the period of the study.
What the researchers did not note in their written text of the results was this - the low-carb dieters had similar declines in their fasting blood glucose levels through month 12, followed by a progressive decline through month 24.
If we look at the data provided, we can see something important changed - the quality of the carbohydrate they consumed seems to have declined. If you look at the table providing details of the dietary intakes, one major change in the low-carb group between moth 12 and month 24 pops out - as the study progressed, the consumed less and less fiber on average, compared with their baseline intake. Now early on, that's to be expected. Later, as carbohydrate is increased - if quality whole foods are the choice - fiber typically increases!
In contrast, insulin levels decreased significantly in participants with diabetes and in those without diabetes in all diet groups, with no significant differences among groups in the amount of decrease.
Among the participants with diabetes, the decrease in HOMA-IR at 24 months was significantly greater in those assigned to the Mediterranean diet than in those assigned to the low-fat diet.
Again, in the text, the researchers do not note if there were changes in HOMA-IR in the low-carb group. There was - over the 24-month period, the HOMA-IR in those with diabetes, following the low-carb diet, declined by 1.0; in those with diabetes following the low-fat diet the decline was 0.3; and in those with diabetes following the Mediterranean diet the decline was 2.3.
The last item reported in the section was the HbA1C levels. Among the participants with diabetes, the proportion of glycated hemoglobin at 24 months decreased by:
0.4 ±1.3% in the low-fat group
0.5 ±1.1% in the Mediterranean-diet group
0.9 ±0.8% in the low-carbohydrate group
The changes were significant only in the low-carbohydrate group.
The lower HbA1C is perhaps one of the most important outcomes of this study. The diabetics, in the low-carb group, were able to lower their levels by 0.9 over the 24 months and this was significantly greater than those in the two other diets. Unfortunately the researchers did not include the baseline HbA1C for participants, so we do not know what the reduction really means.
Tests Changes in bilirubin, alkaline phosphatase, and alanine aminotransferase levels were similar among the diet groups
Alanine aminotransferase levels were significantly reduced from baseline to 24 months in the Mediterranean-diet and the low-carbohydrate groups.
The Good, Bad, and Why oh Why?
Overall, most reporting on the study today, feel the research team did a good job designing the study and executing it, many applauding the high rate of retention in the study for two years. I too am impressed that the participants remained committed to the trial, their assigned diets, and the longer-term outcome measures!
I personally would have liked more information than was published.
Key information regarding the baseline diet was not included in the data - not published items include how many calories were consumed, on average, at baseline; nor do we know how much protein, carbohydrate, fat or fiber was in the baseline dietary habits of those participating. While obviously not critical, it is 'nice to know' data.
I also would have liked to see the researchers have the courage to actually follow the Atkins dietary approach, and not make changes based on a number of assumptions.
We do not, for example, know what the outcome would be if the participants on the low-carb dietary arm had not been told to specifically choose vegetable based fats over animal fats. Atkins does not specifically state you must eat butter, but the diet allows butter. In addition, encouraging the consumption of plant-based proteins over animal proteins is another tweak that may not have had any effect, or may have had a positive or negative one. We simply do not know because the researchers encouraged plant-based protein consumption rather than leave the dietary recommendations as they are - meats, eggs, poultry, fish, tofu and such are allowed, ad libitum. [please see update below!]
The reporting in the media, as my earlier post highlights, has been quite an eye-opener. I'm not sure if those quoted realize it or not, but their reaction to the study is quite telling, especially those with the strongest vested-interests in maintaining the status quo.
In the Wall Street Journal, Robert Eckle, the past president of the American Heart Association and a professor of medicine at the University of Colorado Health Sciences Center, said he was not ready to recommend an Atkins-type low-carb diet based on the results. People on a low-carb diet increased their consumption of saturated fat, he said, which could not be good for them in the long run.
Did he even bother to read the findings?
Or maybe he was just disappointed the AHA's recommended diet - the diet recommendations the low-fat group were instructed to follow - did so poorly compared to the other two?
Did he know that the study author, Dr. Meir Stampfer of Harvard Medical School, in the same article, said "It is time to reconsider the low-fat diet as the first choice for weight loss and for cardiovascular health, it is not the best."
I think tomorrow, we'll take a fun ride through many of the quotes and opinions offered on this study!
In the meantime, what are your thoughts? Feel free to leave comments!
I received an email today from a friend who asked one of the researchers about the reference to plant-based (vegetable) fats and proteins. Dr. Shai assured him that the low carbohydrate group was not advised to consume a vegetarian low-carb diet, nor were they specifically restricted from eggs, cheese, red meat, poultry or fish. Due to dietary restriction (religious) the group would not, for instance have a cheeseburger or butter on top of their steak. Olive oil featured prominently. The participants did read the Atkins diet book. And the examples provided of the types of meals was "For example, a plate could include : fish or fried/not bread coated chicken/or red meet, broccoli and mushrooms coated with eggs, roasted eggplants, vegetable salad (peppers, cucumber, green leaves, notlettuce) with olive oil dressing.