Science & Research: Low Carb Diets vs. Very Low Carb (Ketogenic) Diets
(By Tom Venuto)
Ketogenic low-carbohydrate diets have no metabolic advantage over nonketogenic low-carbohydrate diets.
Johnston CS, et al, American Journal Of Clinical Nutrition. 2006 May;83(5):1055-61. Department of Nutrition, Arizona State University, Mesa, AZ 85212, USA.
Part I: Research Abstract
BACKGROUND: Low-carbohydrate diets may promote greater weight loss than does the conventional low-fat, high-carbohydrate diet.
OBJECTIVE: We compared weight loss and biomarker change in adults adhering to a ketogenic low-carbohydrate (KLC) diet or a nonketogenic low-carbohydrate (NLC) diet.
DESIGN: Twenty adults [body mass index (in kg/m(2)): 34.4 +/- 1.0] were randomly assigned to the KLC (60% of energy as fat, beginning with approximately 5% of energy as carbohydrate) or NLC (30% of energy as fat; approximately 40% of energy as carbohydrate) diet. During the 6-wk trial, participants were sedentary, and 24-h intakes were strictly controlled.
RESULTS: Mean (+/-SE) weight losses (6.3 +/- 0.6 and 7.2 +/- 0.8 kg in KLC and NLC dieters, respectively; P = 0.324) and fat losses (3.4 and 5.5 kg in KLC and NLC dieters, respectively; P = 0.111) did not differ significantly by group after 6 wk. Blood beta-hydroxybutyrate in the KLC dieters was 3.6 times that in the NLC dieters at week 2 (P = 0.018), and LDL cholesterol was directly correlated with blood beta-hydroxybutyrate (r = 0.297, P = 0.025). Overall, insulin sensitivity and resting energy expenditure increased and serum gamma-glutamyltransferase concentrations decreased in both diet groups during the 6-wk trial (P < 0.05). However, inflammatory risk (arachidonic acid:eicosapentaenoic acid ratios in plasma phospholipids) and perceptions of vigor were more adversely affected by the KLC than by the NLC diet.
CONCLUSIONS: KLC and NLC diets were equally effective in reducing body weight and insulin resistance, but the KLC diet was associated with several adverse metabolic and emotional effects. The use of ketogenic diets for weight loss is not warranted
Part II: Discussion
This is a very interesting study that caught my attention because it shows that ketogenic low carb diets, (which are extremely low in carbs, such as Atkins which starts inductions at 20 grams of carbs or less, and others which are definitely under 100 grams a day), are no more effective than moderately low carb diets (such as The Zone or BFFM maximum fat loss phase, etc, which are around 40% carbs or 30% carbs at the lowest, respectively). The extremely low carb / ketogenic diets however, had numerous negative side effects that the more moderate low carb diets did not.
This study, and numerous other studies, has showed greater weight loss with low carb diets than with low fat, high carb diets, at least in the short term, most likely due to automatic reduction in appetite. Long term results (greater than 12 months) are less definitive (because long term compliance seems to be a problem with ALL diets).
Many researchers are opening up to the idea that there may be something to the low carb approach after all. However, the problem with many of very-low-carb studies that report positive findings, as well as the articles, books and news reports in the popular fitness literature that do the same, is that (1) the reason for the added weight loss is seldom explained (is it metabolic advantage or are low carb diets simply better at controlling appetite?), (2) long term compliance is seldom studied or discussed, (3) the "costs" and side effects of extreme carb restriction are seldom highlighted, (4) composition of the weight loss is not always examined (including water loss), and most important, (5) the term "low carb" is seldom defined.
It was these 5 points, particularly the 5th one, for which this study was commissioned. The researchers designed this study to look at the comparative effects of a diet that was referred to as "low carb", but only moderately low in carbs, specifically, 40% of total calories, as in "The Zone" diet, for example, (or the level recommended in BFFM maximum fat loss phase).
Ketogenic diets, on the other hand, are very, very low carb diets such as The Atkins diet, which only allows 20 grams of carbs per day in the initial induction phases. The present study compared the 40% carb diet with a very low carb diet set at 5% of total calories.
In addition to looking at the differences between very low carb (5%) and low carb (40%) diets, this study also wanted to determine the reasons that weight loss is often improved with low carb diets.
Ketogenic diet proponents have longed claimed that there is a "metabolic advantage" that allows one to eat unlimited calories provided carbs are kept below a certain level and or that one stays in ketosis. However, the more likely explanation for increased fat loss while on a ketogenic diet is related to appetite suppression and or a spontaneous reduction in food intake that occurs when carbs are restricted... in other words, the subjects simply ate fewer calories.
The present study confirmed that low carb diets can provide metabolic effects including increased diet-induced thermogenesis (from higher protein, most likely, improved insulin sensitivity and most notably, decreased hunger).
In this study, both groups achieved equal weight loss, which led the researchers to conclude that "the ketogenic very low carb diet did not provide any significant metabolic advantage over the non ketogenic low carb diet."
However, there was an important difference: Researchers found that the very low carb group experienced negative side effects including less vigor and altered mood. This is not surprising as many precontest body builders or low carb dieters will tell you - they can get "fog on the brain" or just plain grouchy when cutting carbs really low.
In previous research, low carb diets have been associated with fatigue, reduced vigor and changes in mood. The present study showed that the group which only restricted carbs moderately experienced greater energy and vigor. This leads us to conclude that moderate carb restriction can provide all the benefits of "low carb" diets without the need for ketosis or extreme carb restriction and so ketogenic diets unnecessary and unwarranted.
On a different note, research supports the concept of re-feeding to prevent metabolic downgrade when dieting. It is likely that those who choose very low carb diets will achieve best results and help reduce negative effects of very low carb dieting by using some form of refeeding or cyclical dieting, with a higher calorie and or higher carb phase, rather than a prolonged intake of very low carbs and very low calories.
Traditional methods of carb/calorie cycling include cyclical ketogenic diets (CKD's) which consist of 5 days in ketosis followed by 2 high carb days, usually on the weekends. Many proponents believe this was an improvement over spending prolonged periods of time on extremely low carbs. Burn The Fat, Feed The Muscle suggests a more moderate cyclical low carb diet of 3 days on moderate low carbs alternated with 1 day of higher carbs and maintenance level calories. Prolonged very low carb diets (without a diet break or carb up/refeed) are likely to be detrimental and difficult to maintain.
Some people seem to respond better to low carbs than others, probably due to genetics and metabolic type. Also, age, obesity and sedentary lifestyle all seem to contribute to decreased glycemic control (these groups show higher incidence of metabolic syndrome and are more likely to be insulin resistant, carb intolerant and even diabetic). Certain people seem to thrive on ketogenic very low carb, high fat diets, while others are hit very hard with negative effects, to the point that they can't even function. Still others experience low energy and mental fogginess during the initial week or two, then seem to adapt eventually as their metabolism appears to accommodate to the switch from carbs to fat.
Last but not least, it's always worth taking a look behind the scenes at who the researchers are and who funded a study. In this case, Barry Sears, author of The Zone (a moderate low carb diet book promoting 40% carb, 30% protein, 30% fat), was a member of the research team, as was Heather Hutchins, an employee of Zone labs. Both Sears and Hutchins contributed to the experimental study design. Obviously the research was undertaken from the beginning to prove the hypothesis that a 40% "low" carb diet is superior to a 5% "very low" carb ketogenic diet.
I think this study attempted to answer a very important question. Previous research only looked at whether a ketogenic diet was more effective than a traditional high carb, low fat diet. But how do a low carb and medium carb diet stack up? Now we know.
I tend to agree with the conclusions of this study as they reinforce my personal real world experiences, and I consider these interesting, relevant and practical findings because in the past "low carb" diets were just lumped together, but obviously there are huge differences in allowed carb intake levels from one program to the next. I also think this is a well-designed study because it controlled for food intake carefully, while previous studies on low carb diets often allowed for self-reporting of food intake which could skew the results.
It must, however, be noted that various forms of bias and conflict of interest can exist in scientific research. Not only can study design and subject selection be manipulated, but also consider this: Let's suppose the Atkins style diet ended up showing greater weight loss results with no side effects in this study. Do you think that this Zone-Diet-sponsored research group would have rushed to get this paper into publication, or would it never have seen the light of day? I wouldn't mind seeing an independent third party repeat this study, (perhaps a study longer than 6 weeks with an even larger test group), to see if they produce the same results. My guess is the answer would be yes.
Part III: Important Take-Aways
1. This study and other studies do show several distinct benefits of reduced carb diets that can help improve weight loss, at least in the short term. the question at hand is, how much do you need to reduce carbs to get these benefits? Science now says: not as much as ketogenic diet proponents think.
2. Be sure you distinguish between moderate carb, low carb and very low carb/ketogenic diets. "low carb" has never been formally defined, and there can be big differences between small reductions in carbs and severe reductions in carbs.
3. Extremely low carb (ketogenic) diets can negatively affect emotion, mood state and the desire to be physically active.
4. Moderate reductions in carbs seem to provide the same benefits as extreme reductions in carbs, without the negative side effects.
5. Carefully controlled research shows no "metabolic advantage" of being in ketosis.
6. Despite all the hype about low carb diets, the primary advantage of any low carb diet is probably the fact that it helps control appetite and it's hard to overeat on a low carb diet. Eat less.... lose weight.
7. Scientific research is often subject to bias. Although it's not necessarily a bad thing if a supplement or diet company funds research, and it may not have any bearing on the findings, it is a possibility to keep in mind.
- Tom Venuto, CSCS, NSCA-CPT