As mentioned before, the literature on weight loss in general and the low carb diet debate in particular is somewhat dishonest and unreliable. This particular article is a research-based article and examines the various claims by the proponents and opponents to the low carb (Atkins diet) pertaining to the risk of cardiovascular disease.
Critics of the low carb, high fat (Atkins) type diets point out that they tend to involve the consumption of high levels of saturated fat. This tends to increase low density lipoprotein (LDL), which is a risk factor for cardiovascular illness.
Comparison of low-carb and low fat / other diets in terms of cardiovascular illness
This particular article looks at a fair number of original research studies and I suggest you don your research hat and pour yourself a cup of coffee before you begin. We are going to examine research studies under 4 main headings, namely:
- research articles demonstrating the positive (or not negative) cardiovascular effects of low carb diets
- meta-analytic studies articles demonstrating the positive (or not negative) cardiovascular effects of low carb diets
- research articles demonstrating negative cardiovascular effects of low carb diets (compared to no diet or other diets)
- meta-analytic studies articles demonstrating negative cardiovascular effects of low carb diets (compared to no diet or other diets)
1. Research articles demonstrating the positive (or not negative) cardiovascular effects of low carb diets
Mozaffarian et al. (2004) conducted a longitudinal study of 235 post-menopausal women over a 3-year period. This was a particularly significant study as its conclusions flew against the breeze of most similar research on saturated fat and heart disease to that point (Knopp and Retzlaff ,2004). In fact Mozaffarian et al. reached the conclusion that ‘In postmenopausal women with relatively low total fat intake, a greater saturated fat intake is associated with less progression of coronary atherosclerosis, whereas carbohydrate intake is associated with a greater progression.’ Of course in low carb diets fat intake is in fact high, but the study was nevertheless ground breaking in terms of its postulations about saturated fat and heart disease.
Halton et al., (2006) analysed health effects in a large sample of female 82 802 subjects over a 20 year period. Their data led them to two important results. Firstly, lower carb (and therefore higher protein and fat) diets did not lead to an increased risk of coronary heart disease in women in their study. Secondly, when vegetable sources of protein and fat were chosen the diet appeared to moderately lower the risk of coronary heart disease. The second conclusion of course does not assert much directly about low-carb diets, but in my opinion it does lend itself to the fairly established argument that animal protein does potentially increase the risk of coronary heart disease, once any variance from carbohydrate levels has been accounted for.
Meta-analysis demonstrating that low carb diets do not negatively affect the cardiovascular system
Ajala et al., (2013) conducted a meta-analysis of the literature comparing low-carbohydrate, vegetarian, vegan, low–glycemic index (GI), high-fiber, Mediterranean, and high-protein diets with control diets including low-fat, high-GI and low-protein diets, in the management of diabetes. The low-carbohydrate, low-GI, Mediterranean, and high-protein diets all led to a greater improvement in glycemic control ( thus lowering the risk of cardiovascular disease and diabetes). However, the Mediterranean diet significantly outperformed the rest. An increase in HDL was seen in all diets except the high-protein diet.
Santos et al., (2012) conducted a meta-analysis to examine the effects of low-carbohydrate diets on weight loss and cardiovascular problems. A total of 23 reports, corresponding to 17 clinical investigations, were identified as meeting the pre-specified criteria. Results showed a significant increase in high-density lipoprotein cholesterol. This study also did not show significant increases in low-density lipoprotein cholesterol. This would potentially support the argument that low-carb diets do not damage the cardiovascular system, or potentially even have a protective effect.
Hession et al., (2007) also conducted a meta-analysis between 2000 and 2006 of low-carb versus low-fat diets. They used similar admission criteria to Nordman et. al., 2006, and obtained 13 studies that they felt met admission criterion. Interestingly enough (and relevant to their conclusions) their criteria appear to have been somewhat less strict than Nordman et al., as they included a lot more studies than Nordman et al. for the overlapping time period. The authors found that over a 6 month period low-carbohydrate diets achieved greater increases in HDL cholesterol and triglyceride levels. The authors also found a higher rate of attrition in groups with low-fat diets. They reported that low-carb diets were ‘as effective, if not more, as LF diets in reducing weight and cardiovascular disease risk up to 1 year’. However, they did note that in some of the low-carb diets the subjects were allowed to increase carbohydrate intake during the diet, which obviously is an obfuscating variable in terms of conclusions drawn as to cardiovascular risk. It is particularly interesting to note that the results and conclusions of the Hession meta-analytic study are significantly different to those of the Nordman meta-analytic study, despite a large overlap in both time period and studies used.
3. Research studies showing that low carb diets damage the cardiovascular system
Anderson et al., (2000) performed a computer simulation (therefore without actual subjects) of eight popular diets and reached the conclusion that ‘The Atkins and Protein Power diets are very high in total and saturated fat compared to current dietary guidelines. Long-term use of these diets for weight maintenance are likely to significantly increase serum cholesterol concentrations and risk for CHD’, and that ‘the potential hazards for worsening risk for progression of atherosclerosis or atherosclerotic events override the short-term benefits’. Of course we need to keep in mind that this was a simulation study.
And why might this be the case? Well, I am always very cautious when we extrapolate too much from animal studies to human studies. Animals are not humans and have their own unique DNA. And equally the proportions of food stuffs to weight to metabolism are difficult things to normalize. Nevertheless, a study by Foo et al., (2009) compared a low-carb high-protein (LCHP) diet with the standard chow diet as well as a ‘Western Diet’ (containing comparable fat and cholesterol to the LCHP diet). They found that that diets low in carbohydrates and high in protein and fats might reduce vascular regenerative capacity and so increase atherogenesis (and therefore cardiovascular risk).
Sjogren et al., (2010) used a sample of 924 men of approximately 71 years of age over a 10-year period to compare how a low-carb diet and a ‘Mediterranean diet’ affect mortality (especially cardiac mortality). They found that a ‘Mediterranean diet’ resulted in significantly decreased mortality, and also significantly fewer cardiovascular related deaths. In contrast the low-carbohydrate diet led to a significantly higher mortality rates as well as significantly higher cardiovascular mortality rates.
Similarly, Lagiou et al.,(2007) followed 42 237 women in the 30-49 age group (at onset of study) over a 12-year period. They concluded that low-carb intake, high protein intake, and a combination of low-carb high-protein intake is ‘associated with increased total and particularly cardiovascular mortality amongst women.’
Ebbeling et al., (2012) compared the Atkins diet, a low-fat high-carb diet and a low glycemic index diet in order to compare resting energy expenditure, total energy expenditure, as well as various other hormonal and metabolic markers. They studied 21 overweight and obese subjects over a 4-year period. The (very) low-carbohydrate diet had the most beneficial effects on energy expenditure and several metabolic syndrome components. However, it also led to increased cortisol excretion and C-Reactive proteins (which is a marker for increased cardiovascular disease). The low–glycemic index diet appears to have qualitatively similar, although smaller, metabolic benefits to the very low-carbohydrate diet, but without the harmful effects on physiological stress and chronic inflammation. They concluded that a diet that focused on reducing glycemic load (as opposed to radically reducing carbohydrates or dietary fat) would probably work best for weight-loss maintenance and cardiovascular disease prevention.
Yancy et al., (2004) found that serum triglyceride levels decreased more and cholesterol levels increased more in the low-carb diet relative to the low-fat diet.
4. Meta-analyses demonstrating that low carb diets negatively affect the cardiovascular system
Noto et al., (2013) conducted a meta-analysis of all studies published from September 2012 to the present in order to examine the long-term effects of low-carb high-protein diets on total mortality and cardiovascular mortality. They concluded that ‘Low-carbohydrate diets were associated with a significantly higher risk of all-cause mortality and they were not significantly associated with a risk of CVD mortality and incidence.’ They further added that the ‘meta-analysis supported long-term harm and no cardiovascular protection with low-carbohydrate diets’, although they cautioned that more long-term studies need to be conducted.
Nordman et al., (2006) conducted a meta-analysis of all studies comparing a low-carb diets without calorie restriction with a low fat diet in individuals with a BMI of at least 25 (i.e. overweight or obese). They had stricter inclusion criteria than the overlapping Hession meta-analysis mentioned above. Analyzing the five studies that met the inclusion criteria they observed that the low-carb diets resulted in ‘potential favorable changes in triglyceride and high-density lipoprotein cholesterol’ values. However, the low-carb diets also led to ‘potential unfavorable changes in low-density lipoprotein cholesterol values’. The authors expressed ‘caution against the conclusion that low-carbohydrate diets can be generally recommended to promote weight loss’. They added that ‘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’.
The quasi-vegetarian low carb diet and cardiovascular mortality
Shai et al., (2008) conducted a 2-year longitudinal study on 322 moderately obese subjects. They compared a low-fat calorie-restrictive diet (based on American Heart Association recommendations in 2000), a Mediterranean calorie-restricted diet, and the Atkins diet (but where the subjects were encouraged to choose vegetable sources of fat and protein to avoid trans fats). In my opinion this version of the Atkins diet is not generalizable to the general population as it is unlikely to be the one followed by most of its supporters at the moment. As such it is not indicative of the standard effect of low carb high fat diets on cholesterol and the cardiovascular system.
However, it is worth including as over the first 2 years drop-out rate was only a shade over 15%, and the quasi-vegetarian low-carbohydrate diet was the only one to significantly improve the HDL to LDL (cholesterol) ratio.
In my opinion the evidence surrounding the effect of low carbohydrate high fat (Atkins) diets on cardiovascular disease is inconclusive. One also has to question how so many, often very similar studies can arrive at such opposing results. In my opinion though there is enough evidence to make me cautious to rush out and embrace a diet high in saturated fats.
If you have read my article on how high protein diets may lead to higher levels of diabetes, cancer and all-cause mortality it becomes apparent that low-carb diets may have other, less apparent negative effects on the risk of developing chronic illness. It makes one wonder if overdosing on any one particular food group doesn’t have potentially worrying long term effects!
A quick mention must be made of the Mediterranean diet that performed superbly in terms of diminishing risk from cardiovascular disease. I also felt that the low GI diet (where one is sacrificing high GI carbs rather than almost all of them) performed admirably here and is worth considering. The ability to consume more carbohydrates (but les high GI ones) translates into not having to consume massively high levels of proteins and fats.
I reckon a low GI, quasi vegetarian diet with reasonable levels of (largely) unsaturated fats and protein might be a great way to go, and would also like to research Mediterranean diets in more detail.
Remember at the end of the day a reduction in daily calories and a healthy, active lifestyle will take you a long way towards losing those extra pounds.
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