The full text is available online here:
Long-term Effects of a Very Low-Carbohydrate Diet and a Low-Fat Diet on Mood and Cognitive Function. Grant D. Brinkworth et al. Arch Intern Med 2009;169(20):1873-1880.
The most significant finding of this study, which seems to have escaped everyone who has written about it, is that it contradicted the earlier, and very heavily publicized, finding that the low carb diet caused problems with memory and thinking.
This year-long study found Working memory improved by 1 year (P < .001 for time), but speed of processing remained largely unchanged, with no effect of diet composition on either cognitive domain.
So that should put to rest any concerns you might have had about the impact of eating a very low carb diet on your ability to think clearly.
Now let's see what else the study found.
Unlike many studies of supposedly "low carb" diets, this diet was indeed a very low carb diet with a composition that matched that described in the most recent Atkins book. The nutrient breakdown was:
4% of total energy as carbohydrate, 35% as protein, and 61% as fat (20% saturated fat), with the objective to restrict carbohydrate to less than 20 g/d for the first 8 weeks and with an option to increase to less than 40 g/d for the remainder of the study.
This study also limited saturated fat which is not characteristic of classic Atkins, but the direction the Atkins brand has moved into as it has come to copy South Beach. Over the years the original "Atkins" diet was modified several times to incorporate the techniques found in other bestselling low carb diet books, so this shouldn't be a surprise.
In one major characteristic this diet differ from Atkins as described in the book. From the outset, calories were restricted to "approximately 1433 kcal/d for women and 1672 kcal/d for men."
Those who wish to ignore the findings of the study completely have pointed to this limitation as if it discredited the results. However, I do not believe this is fair. For overweight and slightly obese people, the calorie levels used here correspond very closely to what many people who have successfully lost weight on the Atkins diet report eating on the online diet support forums, for example, Low Carb Friends once the "easy pounds" lost in the first month or so are gone.
Atkins dieters almost always stall after the first 6 weeks and those who do not have a lot of weight to lose often find they do have to cut back on calories to continue on with weight loss.
So much for the "Atkins diet" used in the study. But when we look at the "low fat" diet, we see something even more interesting. The "low fat" diet is described as having "46% of total energy as carbohydrate, 24% as protein, and 30% as total fat (<8% saturated fat), with the objective to restrict saturated fat intake to less than 10 g/d for the study duration and with the inclusion of an approved food exchange (equivalent to the energy content of 20 g of carbohydrate) between weeks 9 and 52."
This is a very moderate low fat diet, very different from diets like Ornish. And more significantly, this is a diet that is actually quite low in carbohydrate. Working out the 46% ratio of carbohydrate against the 1433 calorie daily intake for women, we find that a woman on this diet would be eating only 165 grams of carbohydrate a day, NOT the 300 grams a day which is so often recommended by dietitians.
This is not an overwhelming carbohydrate intake for a person who has functioning beta cells. And everyone in this study DID have functioning beta cells, since the study excluded people with diabetes, and also eliminated people with cardiovascular disease--which would have probably got rid of participant with undiagnosed diabetes.
The study found that both groups of dieters lost the same average amount of weight at the end of the year, on average about 30 lbs. This full text of the mood study does not explain what the groups starting weights were. This data is probably available in an earlier publication about the same study that reported the physiological rather than psychological findings of this study. You can find it HERE. Unfortunately, free full text is not available for that study.
This earlier report on this same study found that the Atkins dieters ended up with a higher HDL and lower Triglycerides than the Low Fat group, but also higher LDL, though the particle size of the LDL was not investigated.
It also reports the LC group also seems to have lost more body fat: LC: –11.3 ± 1.5 kg; LF: –9.4 ± 1.2 kg; P = 0.3, though this may not be statistically significant.
The physiological study report also found that "Blood pressure, fasting glucose, insulin, insulin resistance, and C-reactive protein decreased independently of diet composition." This means that the choice of diet did NOT have any impact on these parameters though they improved similarly on both diets.
It is a very significant finding that the two diets ended up producing the same blood sugar outcomes, though this has to be viewed with the knowledge that this was a study that did not include people with diabetes.
So far I see nothing to make me question that this was a decently conducted study that has something to teach us about the impact of these diets on people who, if they had any blood sugar abnormalities had the mild ones described as "pre-diabetes"--a group that includes many people who have insulin resistance, but also who have normal beta cells and hence who will never progress to full fledged diabetes.
So what should we make of the finding that mood deteriorated more in people on the Atkins diet than on the low fat diet?
The first thing I note, before I look at mood, is that as is the case in so many diet studies, the drop out rate was high--41%, And slightly more people in the Low Carb arm dropped out than in the Low Fat arm.
This is not the first time we've seen this happen. The drop out rate of the Atkins dieters was only exceeded, very slightly, by that of the extreme Ornish dieters in the JAMA diet bakeoff published back in 2005. In that study the Atkins compliance rate was considerably lower than that of the dieters eating the conventional Weight Watchers diet, though compliance on all diets deteriorated.
This latest study did not measure compliance, but my guess is that by the end of the study, it wasn't very good because it never is on any diet and there is evidence suggesting that "carb creep" is a huge problem, long term, even for people who believe they are eating low carb diets.
But that high drop out rate, with the higher Atkins drop out rate suggests that people eating the diet were not universally thrilled and the mood indicators that the study presents seem to me to point to why.
The study used standardized questionnaires, which like all psychological tools are very fuzzy in concept, but since mood itself is a very fuzzy concept, there isn't any better way to measure it.
The study design has going for it that it used several different tools to measure mood, not just a single one. These were "the POMS,which measures 6 separate aspects of mood, including tension-anxiety, depression-dejection, anger-hostility, vigor-activity, fatigue-inertia, and confusion-bewilderment, and provides a global score of mood disturbance (total mood disturbance score [TMDS]) that is determined by subtracting the vigor-activity score from the sum of the 5 negative mood factors; (2) the Beck Depression Inventory (BDI) and (3) the Spielberger State-Trait Anxiety Inventory (SAI)."
This link will take you to the graphs describing the findings:
Questionnaire Data
What stands out is that the results of all three measurement tools come out with very similar results. At 8 weeks, all the dieters were considerably happier than when they started their diets. And at 8 weeks, the Low carb dieters were MUCH happier than the low fat dieters according to the Depression-Dejection score, probably because the early weight losses on Atkins are much more dramatic and motivating than the losses on the non-ketogenic diet.
By six months things started to change. Both groups were feeling increased Vigor and Activity at six months, probably because that was the time when they had made most of their weight loss and that weight loss made them feel much better about themselves and more prone to physical activity. But by that point, the measurement tools suggest that the mood of the Atkins dieters is beginning to deteriorate compared to that of the people on the low fat diet.
Anyone who has participated in the online Atkins support groups knows that by 6 months most Atkins dieters have either stalled out completely (usually those who are eating very high calorie intakes in the belief that only carbs matter) or they have gone from dramatic weight losses to losing very, very slowly.
You can see exactly how much real dieters lose on a very low carb diet with the analysis of dozens of real people's posted monthly low carb weight loss experiences you'll find HERE.
Slowing weight loss is characteristic of ALL long term diets no matter what the diet composition, but for the Atkins dieter who saw swift weight loss early on in the diet, the slowdown can be devastating, because most Atkins dieters assume that the extreme changes they have to make in what they eat will be rewarded with huge weight losses like those they experience in the first few weeks. When this doesn't happen, the limitations of the diet are much harder to endure.
Experience in the support group environment reinforces the finding that it is at 6 months into the very low carb diet that people run into serious problems with it. The excitement of eating steak, cheese, and avocados has worn off and unless a person is able to cook and willing to put time into hunting up recipes, the food allowed on the diet can become very boring indeed.
And there is another problem, one that is rarely discussed on the Low Carb support boards:. The early high energy level that enthuses people about the very low carb diet may start to fade out. Some people, in fact, experience thyroid slowing (so-called Euthyroid syndrome) characterized by drops in T3.
My guess is that the finding of this study is real, because it mirrors what I've seen in the support groups. After an initial burst of enthusiasm that lasts about 6 months, a large number of low carb dieters disappear. And even those who lose significant amounts of weight tend to disappear shortly after they stall out for a few months or reach goal, only to show up on the support groups a year later with tales of crashing off the diet and regaining all the lost weight.
Because I did the same thing myself, after 3 years on a very low carb diet, I have a very good appreciation of the process that leads from initial enthusiasm, to depression about the need to eat in a way that is so different from what one might want to eat, and the way that dropping energy levels can lead to giving up entirely.
Since I have diabetes and can't process carbs my choice was NOT to say to heck with it and just live with being fat. But people who don't have diabetes can and do.
So I think the mood issue is real and I think that until it is addressed, people will alway have trouble sticking with a low carb diet, long term, no matter what it's impact on their health if it is too extreme.
And it is that factor of extremeness that I think this study sheds some interesting light on.
If we ignore the issue of "fat" which is really a red herring in these two diets, what we see here is that for people WITHOUT diabetes, there may be a much better outcome in terms of mood with a diet that though it restricts carbs a lot compared to the Standard Diet, doesn't restrict them extremely.
In short, for people who do not have diabetes, a diet of 165 g a day is a huge improvement on one of 300 g a day and may be all that is needed. The women eating that 165 grams of carbs a day did lose the same amount of weight and more importantly, their blood sugar profile and blood pressure did not vary from that of the people eating at much lower levels.
For people WITH diabetes this finding is negated by the fact that few of us can tolerate 165 grams of carbohydrate without seeing very poor blood sugars, ones guaranteed to produce complications.
But what I would take from this study is that it supports the strategy I have been promoting for the past 5 years--one that suggests you cut your carbs down ONLY to the level that gives you safe blood sugars, and no lower.
What that level will be varies from person to person and can only be determined using the strategy described HERE.
More importantly, what this study suggests is that if, like me, you find you can only control your blood sugar by eating at extremely low carbohydrate intake levels--for me it was no more than 50 grams a day with no single meal being higher than 12 g--if you start feeling depressed or rundown, it's time to look into finding a medication that will let you raise your carb intake a bit, but still keep hitting your blood sugar targets without making yourself miserable.
For me, the difference between eating at 100 g a day and 50 g a day is that I can do it, year in and year out, happily. (I'm in year 7 of maintaining a 17% loss of body weight.) But I can only eat 100 g a day using fast acting insulin at some meals.
Not EVERYONE gets depressed or exhausted on a long term low carb diet. The people who stay on these diets for years at a time and write the enthusiastic LC blogs are those who feel better on the diet, not worse. There are quite a few people that match that description, especially among those whose blood sugar is hard to control.
But if you run into problems as your low carb diet hits 8 months, or a year, or two, don't fear turning to medication for help. Insulin, metformin, and for some people Byetta, can make a big difference in how easy it is to control your blood sugar and your weight.
Our goal, after all is health but there is little point in purchasing "health" at the cost of your happiness. If after 6 months of eating a very low carb diet your energy level is low and your mood deteriorating, it's time to start tweaking. Talk to your doctor about adding the safe drugs to your regimen.
Too many people treat using medication as if this were a personal failure. It isn't. The safe medications are is just another set of tools to allow you to live a healthy and happy life.
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