A recent Archives of Internal Medicine study by Grant D. Brinkworth et al.`1 assessed changes in mood for dieters on either a low fat or low carbohydrate diet. Study authors concluded that throughout a year of dieting, a low fat plan improved overall feelings of well-being versus a low carb plan. Atkins disagrees with the authors’ interpretation of their results, as the study design provided a low carb diet with an excess of protein and inappropriate limit on salt intake, especially in the weight stabilization phase of the study. As a result, the Brinkworth study offers two cautionary lessons in the management of low carbohydrate diets.
The first lesson is that the prescribed protein intake referred to in this study as a protein intake of 35% of daily food consumed (on average 130 g of protein) is suitable only for the first or Induction phase of Atkins. This prescription, however, becomes inappropriate as people move out of the weight loss phase and into ongoing maintenance, when total food intake must increase to maintain a steady weight. In the six months of weight stability at the end of this study, participants were reportedly still consuming 35% of their daily food intake in the form of protein – for an 80 kg subject that translates to 200-250 grams of protein per day.
This would push the upper limit of human protein tolerance - too high for the weight maintenance phase and liable to lead to a change in mood. Aboriginal hunting cultures such as the Inuit had descriptive terms for the discomfort and unpleasant mood that results from over-consuming protein, and this time-tested observation appears to have been re-discovered in the current study.
Furthermore, Christy Boling Turer, MD, a health services research fellow at the VA Medical Center, in Durham, N.C., notes that twice as many people in the low carb group were being treated for depression at the beginning of the Brinkworth study. According to Turer, that fact, as well as the high dropout rate, suggests that “these data should be viewed cautiously.”
The second lesson is that carbohydrate restriction has long been known to cause a sustained increase in the excretion of salt by the kidneys (natriuresis). If this is counter-balanced by the prescription of a modest daily sodium supplement of 2 grams per day (definitely not a high salt intake), well-being and physical performance are maintained despite the carbohydrate restriction  . Without it, fatigue, lethargy, and headache are common. As both patients and dietitians typically believe in the benefits of restricting salt intake, it is likely that many of the mood and well-being symptoms reported in this study could have been ameliorated by a daily pinch of salt.
In addition, a 2007 study by a different group of researchers showed that after 24 weeks, people on low fat or low carb diets both showed improvements in mood, but the improvements were greater in the low carb group. Eric C. Westman, MD, of the Lifestyle Medicine Clinic at Duke University Medical Center, in Durham, N.C., who helped conduct the 2007 research, says the two studies have one key difference. In his study, people on a low carbohydrate diet were allowed to eat as much as they wanted.
“The main difference between their methodology and our study methodology was that they restricted the amount that people could eat and we did not,” Dr. Westman says. “That’s an important thing to focus on because…if you’re told you can’t eat as much as you want, this may put some damper on the mood, so to speak.”
A low carbohydrate diet can be safe and sustainable if managed with a modicum of care through both the weight loss and maintenance phases, which differ in a number of aspects. However the over consumption of protein and inappropriate sodium restriction, as apparently practiced in this study, indicate that we ignore these lessons of history at our peril.
 Brinkworth, GD et al. Arch Int Med. 2009;169:1873-80. Gamble JL et al. J. Biol. Chem. 1923; 57: 633-695. Phinney SD, et al. J Clin Invest. 1980;66:1152-61. Phinney, SD, et al. Metabolism. 1983;32:769-76.