- Dueling Diets: Low-Carb Equals Low-Fat for Weight Loss but Boosts Cholesterol
- Low carb diets help weight loss, but may raise cholesterol
- 'No evidence' low-carb diets are good for your heart
- Atkins diet hikes 'bad' cholesterol levels
The articles all try to disseminate the review published yesterday in the Archives of Internal Medicine, Effects of Low-Carbohydrate vs Low-Fat Diets on Weight Loss and Cardiovascular Risk Factors (Arch Intern Med. 2006;166:285-293), led by researchers from the University Hospital Basel, Switzerland.
The conclusions, from the abstract - Conclusions Low-carbohydrate, non–energy-restricted diets appear to be at least as effective as low-fat, energy-restricted diets in inducing weight loss for up to 1 year. However, potential favorable changes in triglyceride and high-density lipoprotein cholesterol values should be weighed against potential unfavorable changes in low-density lipoprotein cholesterol values when low-carbohydrate diets to induce weight loss are considered.
Later, in the discussion section of the full-text, we find the following ominous warning: In our opinion, the unfavorable changes in LDL-C levels caution against the conclusion that low-carbohydrate diets can be generally recommended to promote weight loss. No trials of low-carbohydrate diets have been performed that are powered for clinical end points (eg, myocardial infarction or death). It is therefore uncertain whether the beneficial effects of these diets on HDL-C and triglyceride levels outweigh the unfavorable changes in LDL-C level. In contrast, trials of reduced-fat diets, in conjunction with other lifestyle modifications such as increased physical activity, have demonstrated long-term maintenance of weight reduction and delayed onset of diabetes. Furthermore, randomized controlled trials have also demonstrated the benefits of the Mediterranean diet on secondary prevention of cardiovascular disease.
As I started to read through the paper, one thing was clear, the analysis was short-sighted and failed to include important additional information - namely the improvement or decline in cholesterol ratios, a standard used by clinicians to determine one's risk of heart disease. There are two such ratio calculations that may be used - the TC/HDL ratio (total cholesterol to HDL) or the LDL/HDL ratio.
I'm not sure why the researchers failed to include this data, but it is quite revealing and should have been included. You'll see why in a moment...first let's look at the studies included:
- Brehm BJ, Seeley RJ, Daniels SR, D’Alessio DA. A randomized trial comparing a very low carbohydrate diet and a calorie-restricted low fat diet on body weight and cardiovascular risk factors in healthy women. J Clin Endocrinol Metab. 2003;88:1617-1623.FULL TEXT
- Foster GD, Wyatt HR, Hill JO, et al. A randomized trial of a low-carbohydrate diet for obesity. N Engl J Med. 2003;348:2082-2090.FULL TEXT
- Samaha FF, Iqbal N, Seshadri P, et al. A low-carbohydrate as compared with a low-fat diet in severe obesity. N Engl J Med. 2003;348:2074-2081.FULL TEXT
- Stern L, Iqbal N, Seshadri P, et al. The effects of low-carbohydrate versus conventional weight loss diets in severely obese adults: one-year follow-up of a randomized trial. Ann Intern Med. 2004;140:778-785. FULL TEXT
- Yancy WS Jr, Olsen MK, Guyton JR, Bakst RP, Westman EC. A low-carbohydrate, ketogenic diet versus a low-fat diet to treat obesity and hyperlipidemia: a randomized, controlled trial. Ann Intern Med. 2004;140:769-777.FULL TEXT
- Dansinger ML, Gleason JA, Griffith JL, Selker HP, Schaefer EJ. Comparison of the Atkins, Ornish, Weight Watchers, and Zone diets for weight loss and heart disease risk reduction: a randomized trial. JAMA. 2005;293:43-53.FULL TEXT
To compare the data, they followed a very simple approach - actual numbers from baseline to six months or baseline to one-year and measured individually the changes in Total Cholesterol (TC), LDL, HDL and Triglycerides (TG). And quite frankly, when we review this simplistic analysis, things do indeed look bleak for the low-carb diet's impact on cholesterol levels.
But what's missing?
Ahhh...the baseline ratios compared with the follow-up ratios or TC to HDL! This is an important ratio to pay attention to - when a diet causes the ratio to decrease, that's good - if it causes the ratio to increase, that's bad. When comparing two dietary approaches, looking at the impact each has on the baseline ratio to the follow-up ratio is, in my opinion, a much better determinant of how the diet is increasing or decreasing risk of something like cardiovascular disease. And, I'm not alone with this thinking - in fact, studies support that "In addition to LDL cholesterol, the total to HDL cholesterol (TC/HDL) ratio is one of the most potent lipid predictors for cardiovascular disease."
What do these ratios look like? How about we take a look now...
What does the data now tell us?
On average, at six-months, those following a low-carb diet improved (lowered) their TC/HDL ratio by 13% compared to the low-fat diet improvement of 6.6%. Add to this, those on low-carb averaged a 24.6% decrease in their triglycerides compared with the 6.8% decrease by those following low-fat - a more than three-fold improvement in the low-carb group.
On average, at one-year, those following a low-carb diet improved (lowered) their TC/HDL ratio by 7.6% compared to the low-fat diet improvement of 6.8%. Add to this, those on low-carb averaged a 19.6% decrease in triglycerides compared with a 7% decrease by those following low-fat - more than a two-fold improvement in the low-carb group.
What none of this data can tell you though is if the subjects actually ate a low-carb diet!
Unfortunately Foster et al doesn't include macronutrient consumption in their paper, but all the other authors did. While the inclusion criteria in the present review stated that the data reviewed would meet this criteria: To be included in this meta-analysis, trials were required to use a randomized controlled design comparing the effects of a low-carbohydrate diet (defined as a diet allowing a maximum intake of 60 g of carbohydrates per day) without energy intake restriction vs a low-fat diet (defined as a diet allowing a maximum of 30% of the daily energy intake from fat) with energy intake restriction in individuals with a body mass index (calculated as weight in kilograms divided by the square of height in meters) of at least 25.
We find instead that the stubjects in the studies were actually eating more carbohydrate:
At the six month follow-up, subjects following "low-carb" were consuming:
- Samaha 150.7g carb 37.8% of calories
- Yancy 29.5g carb 8.0% of calories
- Dansinger 190.0g carb 41.1% of calories
- Brehm 98.6g carb 39.7% of calories
At the one-year follow-up, subjects following "low-carb" were consuming:
- Stern 120.0g carb 32.8% of calories
- Dansinger 190.0g carb 40.2% of calories
Once we begin to really look at this data, we now understand that with the exception of one (maybe two if subjects in Foster et al consumed less than 60g of carbohydrate each day) that this review isn't really a meta-analysis of low-carb diets versus low-fat diets, but controlled-carb diets versus low-fat diets.
This is an important distinction since the evidence thus far tells us that strictly controlling carbohydrate - to truly "low-carb" levels of 60g or less of carbohydrate a day - does have an even greater capacity to improve TC/HDL ratios and triglycerides.Generally, it is understood within the scientific community that low-carb diets must be no more than 60g of carbohydrate a day to be deemed "low-carb" and that higher intakes of carbohydrate that remain at or below 40% of energy from carbohydrate are not "low-carb" but "controlled-carb" or "carbohydrate restricted."
The researchers of this particular paper failed to note the carbohydrate level consumed or its potential relation to cholesterol outcomes.
They also failed to really do the important work of examining whether these controlled-carb diets improved overall TC/HDL ratios. As we see above, they did and much more so than the low-fat diets.
When we take the overall improvements in TC/HDL ratios and also look at improvements in triglycerides, who can say with a straight face that controlled-carb isn't a better better approach?