One of the longest running debates in the field of nutrition is whether specific diets, especially low-carbohydrate diets, have a “metabolic advantage”. By this I mean that they can somehow cause more fat loss at the same calorie level as other diets. A recent study looking at different types of diets in pre-menopausal women is currently making the rounds and people are using it to claim exactly that. So let’s look at the following study in some detail:
Gardner CD et. al. Comparison of the Atkins, Zone, Ornish, and LEARN diets for change in weight and related risk factors among overweight premenopausal women: the A TO Z Weight Loss Study: a randomized trial. JAMA. (2007) 297(9):969-77.
Low-Carbohydrate Diets and the Metabolic Advantage
As I said above, a long-standing debate is over whether or not specific diets, especially low-carbohydrate diets have a metabolic advantage. This is an idea that came out of very early, very poorly done research where water loss was confused with real weight and fat loss. But it’s an idea to persist to this day.
And by and large, controlled research simply does not support the existence of this metabolic advantage. It’s only when calories are uncontrolled and people end up eating different amounts of protein and calories that one seems to appear.
But the paper I want to examine today, examining four different diets in pre-menopausal women is being used to make that argument yet again. Several fitness related blogs have stated that the Atkins/very-low carbohydrate diet generated significantly greater weight losses based on it. As you’ll see the claims that were made based on the results aren’t quite as astounding as many made them out to be.
Before continuing, I want to address a concern that is invariably raised when I do articles like this which is that I am somehow against low-carbohydrate diets because I don’t think they have a metabolic advantage. Frankly, this is laughable.
My first book The Ketogenic Diet was dedicated to nothing but low-carbohydrate diets and many of my diet books incorporate some type of carbohydrate restriction since that is the reality of creating a sufficient deficit once protein is set at the right place.
Like all diets, low-carb diets have their time and place, pros and cons, benefits and drawbacks. As I wrote about in The Women’s Book Vol 1, there are specific situations such as in PCOS and others where low-carbohydrate diets are likely to be superior.
But that doesn’t have anything to do with whether or not such diets have a metabolic advantage in terms of generating more fat loss which is simply not supported by the bulk of controlled diet studies. It’s simply a logical approach to take in a situation where someone is insulin resistant.
The Impact of Different Diets on Obese Premenopausal Women
Which brings us to this week’s study. The researchers set out to compare 4 diets of drastically different carbohydrate intake. The first was The Atkins diet which is a very low-carbohydrate (50 grams per day or less). The second was The Zone Diet which is a moderate carb diet (40% carbs, 30% protein, 30% fat).
The third is something called the LEARN diet which is your basic food Pyramidy type of diet with 55-60% carbs and saturated fat below 10% of total calories. Finally was Dean Ornish’s extremely high-carbohydrate, very low-fat (10% or less) diet. These diets were chosen to represent the spectrum of diets from very low carbohydrate to very high carbohydrate which I daresay they did.
The subjects were premenopausal women between the ages of 25-50 with a body mass index between 27 and 40 who had been weight stable for the previous 2 months. Other exclusion 311 subjects entered the study and were randomly assigned to one of the four groups with about 70 subjects per group. This is actually fairly large so far as diet studies go which is good as it helps to give it better statistical power.
All subjects were given a copy of the respective book and a dietitian explained the details of the diet to each. For the first 8 weeks of the study, all subjects attended a 1 hour class per week. For the remaining 10 months of the study, they were on their own.
Subjects did receive email and phone contact from the staff between the 2 and 6 month mark and the 6 and 12 month mark and small financial incentives were given for completing the data collection at the 2, 6 and 12 month time point.
Diet was assessed by a 3 day food recall (I’ll come back to this below) and energy expenditure was estimated by a 7 day activity recall. Subjects were measured for height, weight, body fat was done by DEXA. A number of blood measures including total cholesterol and blood triglycerides were measured. So was fasting insulin and blood glucose along with blood pressure.
The Diet’s Results
Ok, before getting into the details, I want to look at the overall results since that’s most of what people focused on. After 12 months on the diet, the respective weight losses were
- Atkins: 4.7 kg (10.3 lbs)
- Zone: 1.6 kg (3.5 lbs)
- LEARN: 2.6 kg (5.7 lbs)
- Ornish: 2.2 kg (4.8 lbs)
So yes, the Atkins group did get better results, 2.5 kg or more weight loss than the other diets over the span of a year. And, according to the self-reported food intakes (an issue that I’ll discuss momentarily), they did it eating the same number of calories as the other groups with both groups reporting a reduction in food intake over the length of the study. Aha, the pundits say, the women got more weight loss on the same calories with the Atkins diet, there’s your metabolic advantage….
Ok, first and foremost, let’s be realistic: regardless of the fact that Atkins got double the weight loss, those results suck. Ten pounds weight loss in one year amounts to a 3/4 lb weight loss per month in the Atkins group and half or less than that in the other groups.
By contrast, low-calorie diets that are highly controlled can generate a 7kg/15 lb weight loss over 4 weeks. My own Rapid Fat Loss Handbook can do that in 2 weeks in some people.
Now there is no doubt that even small weight losses, as little as 10% from current weight, improves health. But I doubt many dieters would be happy with such a paltry weight loss in a year’s time. Most would want 10 lbs in 2 months, a number I didn’t pick out of a hat.
Yes, fine, the study points out that even small weight losses can improve health but what dieter would be happy with that? Not many. More like 10 lbs weight loss in 2 months. I didn’t pick that value out of a hat.
The paper shows changes in body weight at each of the 2, 6 and 12 month time spans. And Table 3 in the paper, which I show below shows how each diet affected weight. And when you see the pattern, it tells the entire tale of what really happened.
The main take-home here is that the Atkins diet was already about 2 kg (4.4 lbs) ahead of the other diets at the 2 month mark with a weight loss of about 4.5 kg compared to about 2.5 kg Now recall from the overall results that the Atkins diet ended up with about 2.5 kg more weight loss than the other groups after a year. You can see that in the chart too where the other three diets range from 1.5-2.5 kg weight loss and the Atkins diet is just shy of 5 kg.
So let me restate that. At the 2 month mark, the Atkins diet was about 2 kg ahead. After a year, they ended up 2.5 kg ahead. Almost the entirety of the “advantage” occurred in the first 2 months. The biggest difference actually occurred at the 6 month mark but it was lost by month 12. What’s going on?
Rapid Water Loss on Ketogenic Diets
Now, it’s well-established that ketogenic diets can cause significant water loss in the first couple of weeks, water loss can range from 1-15 lbs over that time frame. I’m a little guy but I can drop 7 lbs in 3 days of carbohydrate restriction or about 2.5 kg. Larger individuals can lose even more than that. But this is what the supposed “metabolic advantage” of ketogenic diets ultimately came down to: rapid early water weight loss.
Which leads to the logical conclusion that the 2kg “advantage” of the Atkins diet not only could be due to water loss but is most likely due to water loss. Other studies, lasting from 4 days to 2 weeks show the same 2kg difference in weight loss. All of which occurs early on and likely represents water drops due to carbohydrate restriction.
The Pattern of Weight Loss
Another interesting point is that over the next 10 months, the Zone, LEARN and Ornish group didn’t lose an additional pound and even showed a slight trend towards regain. Read that and let it sink in for a few minutes. Over a 12 month diet, after a small weight loss in the first 2 months, there was no additional weight loss for the next 10 months. For any diet, regardless of type, this is pretty terrible results wise.
Rather, the entirety of their weight loss occurred during the first 8 weeks when they went to weekly meetings and they didn’t lose an ounce for the remaining 10 months. In contrast, the Atkins group had lost about 2 kg more at the 6 month mark and regained over a kilogram at the 12 month mark, leading to the final results reported above.
Self Reported Food Intake is Terrible
As mentioned, the groups all self-reported eating roughly the same number of calories and reducing their caloric intake over the length of the study. But let’s think about that rationally for a second: are we to honestly believe that the three groups which didn’t lose an additional pound over 10 months truly ate less over that time period?
Was every single person in this study one of the metabolic miracles that exist in droves on the Internet, that can eat less let magically maintain weight?
Or is it more likely, as with tons of studies done previously, that they were under-reporting their food intake and actually eating more (possibly quite a bit more as studies of carb based diets show a systematic under-reporting of anywhere from 30-50%) than they thought or said they were? Here’s a hint: it was under-reporting.
Now, call me a cynic but I think you know where my opinion on this lays. Studies where calories are strictly controlled and protein intake is matched NEVER show the results that this study does. Ever. It’s only when calories and protein are uncontrolled that this ever shows up. And that’s interesting.
Simply, self-reported food intakes are garbage. It’s why nutritional epidemiology is crap.
So even was slightly greater for the Atkins diet, given the bulk of the data on the topic, it’s unlikely due to any inherent “metabolic advantage”. Rather it’s the combination of a rapid water loss early in the diet and the fact that, under uncontrolled conditions, people on ketogenic diets tend to automatically eat less.
They don’t even have to have eaten much less than the other diets to explain the results of this study. An additional loss of 5 true pound of fat over a year (the 2.5 kg difference) only requires a 50 calorie difference in intake than the other diets. No self-reported food intakes could pick up this small of a difference.
I should mention that based on the self-reported food intakes, a lot of the criticism of this study has to do with overall compliance to the actual diets. For example, Ornish has complained that the dieters were eating 30% fat when he prescribes only 10% fat. Hence it wasn’t his diet. And the Atkins dieters were eating almost 35% carbs at the end of the study. So it wasn’t really an Atkins diet.
There is some truth to this and does raise some questions about the inherent validity of the study. However, it also raises the point that, in free living subjects, people usually suck at adhering or properly following diets. So even with those flaws, this study probably represents how people actually diet in the real world.
And what was seen is what was seen. The Atkins diet showed a rapid early weight loss and then regained it by the end of the study ending up with a whopping 2.5 kg difference after a year. If that’s a “metabolic advantage” it’s not much of one. And it’s certainly nothing to pin the superiority of a given diet on so far as I’m concerned.
I should mention that some of the health measures (blood lipids, etc) did show a slight advantage to one or the other diets but the differences were small and hardly significant. You could generate more changes with just about any reasonable diet that actually too a decent amount of weight/fat off of someone than with the pitiful results this study found.
First, what I’m not saying. As usual, folks will find a way to read this as “Lyle dislikes low-carbohydrate diets” which is incorrect. People need to stop confusing writing factually abut something being against it. Stop being stupid. Like all dietary approaches they have their pros and cons and are appropriate in some conditions and not in others.
For many people, they make controlling calories easier, for people with insulin resistance they often improve health parameters to a greater degree than carb-based diets. Those are advantages to be sure but they aren’t the ones that most are fixated on (e.g. the idea that you’ll somehow lose tons of weight and fat while ignoring caloric intake).
Clearly, despite some of the current claims, simply reducing carbs doesn’t magically “cure” obesity if calories don’t come down. And studies like this demonstrate that. Even if the Atkins diet was slightly superior to the other diets, the simply fact is that the overall weight loss was minor in all groups (this is a common finding among many studies where caloric restriction per se really isn’t put into place).
Ten pounds total weight loss (or even true fat loss) in a year of dieting is crap results, plain and simple. Whether or not it was slightly better than the other approahches wouldn’t seem to be that massively significant.
Especially when you consider that 8 of those 10 pounds occurred in the first 2 months, meaning that there was only 2 lbs more net weight loss over the next ten months of the study (the equivalent of 0.2 lbs weight loss per month).
Because while you some have parsed this study as showing that the Atkins diet has a metabolic advantage you could equally parse it as showing that most diets generate terrible results no matter how they are set up.