Effects of Low-Carb Diet on the Heart and Arteries

These listings are quoted from scientific and medical journals. At then end of each listing, you'll find an expanation in jargon-free English. Every effort was made to keep the explanations true to the original article. However, bear in mind that the explanations were not written by a medical professional, and may contain errors. In a few places, I added my own thoughts. I've tried to mark what's my opinion and what is fact. Let us know if you have any suggestions for improvements or corrections.

Sincerely, Joshua M. Yelon

Differential effects of various oil diets on the risk of cardiac arrhythmias in rats.

Isensee H, Jacob R. Institute of Physiology II, University of Tubingen, Germany.
J Cardiovasc Risk 1994 Dec;1(4):353-359

BACKGROUND: Independently of the problem of atherogenesis, the amount and type of fat intake influences the risk of cardiac arrhythmias. However, the relative effectiveness of different fats and the underlying mechanisms are controversial. The aim of the present study was to compare the effects of various oil-enriched diets on the risk of ventricular arrhythmias in rat hearts under conditions of ischaemia and reperfusion and to help clarify the mechanisms underlying the differing effects of the oils on the occurrence of arrhythmias. METHODS: Over a 10-week period, we studied five groups of young male Wistar rats given a low-fat chow diet or one enriched with 10% hydrogenated coconut oil, corn oil, linseed oil or sardine oil. Electrocardiograms were recorded from the isolated hearts (Langendorff preparation) perfused with a modified Krebs-Henseleit solution. Ischaemia was induced by a 20 min occlusion of the left anterior descending coronary artery. In another series of experiments, a 10 min occlusion was followed by a 20 min reperfusion period. The times between the first occurrence of extrasystole and the incidence of ventricular tachycardia and fibrillation were determined. The size of the ischaemic zone was assessed using malachite green. The fatty acid composition of the myocardial tissue was analysed using gas chromatography. RESULTS: An increase in the risk of ventricular arrhythmias under conditions of both ischaemia and reperfusion was obvious in the rats that consumed large quantities of saturated fatty acids (coconut oil) and in the group with a very low intake of fat. Polyunsaturated fatty acids (PUFAs), particularly fish oil, exerted a protective effect. The incidence of ventricular fibrillation was 75% in the low-fat group, 67% in the coconut-oil group, 44% in the corn-oil group, 40% in the linseed-oil group and 10% in the fish-oil group. The time until the first occurrence of extrasystole, the incidence of ventricular tachycardia and the incidence of reperfusion-induced ventricular fibrillation were influenced in a similar manner. The size of the ischaemic zone was significantly reduced in the groups given diets enriched with PUFAs. All protective effects were abolished, however, by cyclooxygenase inhibition with aspirin. The fatty acid composition of myocardial tissue, the ratio of n-3 to n-6 fatty acids and the double-bond index were significantly affected by the various diets. CONCLUSION: Whereas saturated fatty acids are obviously proarrhythmic, diets enriched with n-6 or n-3 PUFAs both exert antiarrhythmic effects. Although n-3 fatty acids seem to be more effective, cardioprotection cannot simply be related to the replacement of n-6 by n-3 fatty acids in cardiac membrane phospholipids, given the beneficial effects of corn oil. In any case, replacement of n-3 by n-6 fatty acids is not the underlying mechanism. The overall reduction of prostaglandin formation cannot be the primary mechanism because the beneficial effects of diets rich in PUFAs were abolished by cyclooxygenase inhibition. We conlcude that, besides prostacyclin (PGI2 or PGI3), membrane fluidity and accompanying alterations in functional membrane proteins (e.g. protection from calcium overload) are key factors apart from vascular effects that influence the size of the ischaemic zone.

Comments: They wanted to know: can a good diet give you a stronger, steadier heartbeat? They got some rats, and fed them different things. Then, they used clamps to irritate the rats' hearts, trying to get them to skip a beat. Some of the rats had steady heartbeats that just kept going strong, even though they were being irritated. The hearts of the rats who had been fed fat were steadier than the hearts of the rats who had eaten low-fat. Here are the exact numbers. Group 1 was fed low-fat rat chow --- 75% of them skipped a beat. Group 2 was fed rat chow plus partially hydrogenated coconut oil --- 67% of them skipped a beat. Group 3 was fed rat chow plus corn-oil --- 44% of them skipped a beat. Group 4 was fed rat chow plus linseed oil --- 40% of them skipped a beat. Group 5 was fed rat chow plus sardine oil --- 10% of them skipped a beat. Remember, none of these diets was low-carb. This only goes to show, fat may be better for your heart than some people think, especially the fat in fish. The article also says quite a bit about why some kinds of fat are good for the heart, although I didn't understand that part, and I could use some help.

Weight-loss with low or high carbohydrate diet?

Golay A, Eigenheer C, Morel Y, Kujawski P, Lehmann T, de Tonnac N. Department of Internal Medicine, University Hospital Geneva.
Int J Obes Relat Metab Disord 1996 Dec;20(12):1067-1072

OBJECTIVE: With obesity being recognized as an important cardiovascular risk factor, it is important to determine the optimal hypocaloric diet for decreasing that risk. The goal of this study was to compare the effects of two hypocaloric diets of similar caloric value, but differing in carbohydrate content (25% and 45%). SUBJECTS: Sixty-eight out-patients were followed for 12 w. DESIGN: The patients were assigned to one of two groups that received either a low (25% CHO, n = 31) or a high (45% CHO, n = 37) carbohydrate hypocaloric diet (5.0 MJ/d, 1200 Kcal/d). RESULTS: After 12 w, the mean weight loss was similar and did not differ significantly between the two groups: 10.2 +/- 0.7 kg (25% CHO) and 8.6 +/- 0.8 kg (45% CHO). Furthermore, loss of adipose tissue was similar, 8.1 +/- 0.5 kg (25% CHO) and 7.1 +/- 0.7 kg (45% CHO). Despite a high protein intake (1.4 g/kg/ideal body weight) there was loss of lean body mass: 2.2 +/- 0.4 kg (25% CHO) and 1.4 +/- 0.3 kg (45% CHO). The waist/hip ratio diminished significantly (P < 0.001) and identically in both groups. The fasting blood glucose (even though normal, along with cholesterol and triglyceride concentrations, were significantly decreased after weight loss. The fasting blood insulin which was mildly elevated before weight loss decreased more markedly with the 25% CHO diet compared to the 45% CHO diet (P < 0.003). The glucose/insulin ratio improved significantly (P < 0.05) after weight loss with both diets (0.17 +/- 0.04 mmol/mU (25% CHO) vs 0.10 +/- 0.03 mmol/mU (45% CHO). CONCLUSIONS: Neither diet offered a significant advantage when comparing weight loss or other, metabolic parameters over a 12 w period. However, considering the greater improvement of fasting blood insulin, the glucose/insulin ratio and blood triglyceride, the low carbohydrate diet (25%) could be more favourable in the long-term. The improvement of fasting blood insulin could be explained by the differences in monounsaturated fat composition in the low carbohydrate diet.

Comments: 68 people were split into two groups: half received a low-carb diet, the other received a high-carb diet. The low-carbers ended up with lower triglycerides, the high-carbers ended up with lower cholesterol. These researchers judged the triglycerides more important, so they like the low-carb diet better.

Weight loss with high and low carbohydrate 1200 kcal diets in free living women.

Lean ME, Han TS, Prvan T, Richmond PR, Avenell A. University of Glasgow, Department of Human Nutrition, Glasgow Royal Infirmary, UK.
Eur J Clin Nutr 1997 Apr;51(4):243-248

This randomised controlled trial examined anthropometric changes and cardiovascular benefits of six months of weight management in 110 free living women, aged 18-68 y and BMI 25-50 kg/m2, who received 1200 kcal/d diet treatments of either high (58% energy, n = 57) or low (35% energy, n = 53) carbohydrate (CHO) content. Body weight, plasma total, HDL and LDL cholesterol, triglyceride and blood pressure were measured. Examination at three months showed women on high CHO lost (mean +/- s.e.m) 4.3 +/- 0.5 kg and those on low CHO lost 5.6 +/- 0.6 kg of body weight. Changes in risk factors did not significantly differ between the two diet treatments throughout the study. However those on high CHO diets significantly lowered their plasma total cholesterol by 0.33 mmol/l (95% CI: 0.10, 0.55), LDL cholesterol by 0.23 mmol/l (0.02, 0.43) and HDL cholesterol by 0.05 mmol/l (0.03, 0.10), while women on low CHO diets lowered only plasma triglyceride by 0.28 mmol/l (0.08, 0.48). Blood pressure did not change significantly on either diet. After six months, women on high CHO lost 5.6 +/- 0.8 kg and those on low CHO lost 6.8 +/- 0.8 kg. On the high CHO diet, total cholesterol remained significantly below the baseline value at 0.34 mmol/l (0.13, 0.56), triglyceride was significantly lowered by 0.27 mmol/l (0.10, 0.45), and HDL cholesterol returned to the baseline value. On the low CHO diet, triglyceride remained the only risk factor to be significantly improved. A subgroup of 46 postmenopausal women lost significantly (P < 0.05) more weight on the low CHO diet than high CHO diet. In conclusion, these results provided some support for preferring a high CHO diet to a lower CHO approach in weight management, from the point of view of risk reduction, but do not indicate a consistently more rapid weight loss with either diet.

Comments: 110 women were split into two groups: half got a low-carb diet, the other half, a high-carb diet. The high-carb group ended up with lower cholesterol levels, the low-carb group ended up with lower triglycerides. These two differences balanced each other out leaving no overall difference in heart-attack risk. The researchers liked the high-carb diet better, based on the fact that they think cholesterol's more important than triglycerides in terms of heart-attack risk.

A randomized controlled trial of low carbohydrate and low fat/high fiber diets for weight loss.

Baron JA, Schori A, Crow B, Carter R, Mann JI
Am J Public Health 1986 Nov;76(11):1293-1296

Among 135 overweight subjects, we conducted a three-month randomized controlled trial of two sets of dietary advice, each providing approximately 1,000 calories per day but differing in fiber, carbohydrate, and fat content. Information on weight and eating habits, as well as measures of lipoprotein and glucose metabolism were obtained at entry and one and three months later. We found that dieters given low carbohydrate/low fiber dietary advice tended to lose more weight than those given a higher carbohydrate/higher fiber regimen (5.0 vs 3.7 kg on average at three months). This pattern was particularly marked among women, and among participants who were under age 40 or of lower social class. There were no differences between the diet groups in the proportion complaining of hunger but, in general, members of the low carbohydrate group complained of more problems in dieting. There were only minor differences in the serum lipoprotein patterns during the diet period. In view of these results, we believe previous claims of the benefits of fiber for weight loss may have been overstated.

Comments: they got 135 overweight people, and split them into two groups. They told half to eat 1000 calories of low-carb food. They told the other half to eat 1000 calories of high-carb food. After 3 months of this, cholesterol and triglycerides were the same between the two groups.

Effects of ingestion of high protein or excess methionine diets by rats for two years.

Fau D, Peret J, Hadjiisky P Centre de Recherches sur la Nutrition, CNRS, Meudon-Bellevue, France.
J Nutr 1988 Jan;118(1):128-133

Eighteen male Wistar rats weighing 230 g (9 wk old) were fed casein diets containing 10% protein (HC), 50% protein (HP) or 10% protein plus 2% DL-methionine (MET) for 2 yr. In HC rats, mean body weight was 570 g; the carcass contained 13.5% protein and 37% lipid. The HP-fed rats had a 100 g lower body weight than HC rats due solely to a smaller amount of body lipid. Liver urea concentration and kidney weight were higher in HP rats than in HC rats. The body weight of MET-fed rats was lower than the other two groups and body lipid was only 30% that of HC rats. Histologic examination showed a normal aspect of the thoracic aorta from HC rats, whereas in HP, moderate signs of vascular aging--thicker intima and media with hypertrophy of smooth muscular cells (smc) with collagen enrichment and diffuse fibrosis--were observed. Aortas from MET rats also exhibited thicker intima and media due to smc hypertrophy. Some smc presented degenerative aspects and necrosis; other smc were replaced by chondroid cells and foci of fibrosis, resulting in a loss of the distension capacity of the aorta. Such an advanced stage of vascular aging is not normally found in 2-yr-old rats.

Comments: they fed six young rats a low-protein diet, and six young rats a high-protein diet. After 2 years, the high-protein rats showed some hardening of the arteries, which is unusual in young rats like these. It remains to be seen if this effect occurs in humans. Rats seem to handle protein poorly. I think they just weren't evolved for it.

The transient hypercholesterolemia of major weight loss.

Phinney SD, Tang AB, Waggoner CR, Tezanos-Pinto RG, Davis PA
Am J Clin Nutr 1991 Jun;53(6):1404-1410

Serum lipoproteins, body composition, and adipose cholesterol contents of six obese women were studied during and after major weight loss by very-low-calorie diets (VLCDs). Subjects started at 168 +/- 11% of ideal body weight, lost 30.3 +/- 3.7 kg in 5-7 mo, followed by 2+ mo in weight maintenance. Serum cholesterol fell from a prediet (baseline) value of 5.49 +/- 0.32 to 3.62 +/- 0.31 mmol/L (P less than 0.01) after 1-2 mo of VLCDs (nadir), after which it rose to 5.95 +/- 0.36 mmol/L (peak, P less than 0.01 compared with nadir and baseline) as weight loss continued. With weight maintenance, serum cholesterol fell to 4.92 +/- 0.34 mmol/L (P less than 0.05 compared with peak). Adipose cholesterol content did not change in peripheral (arm and leg) biopsy sites but rose significantly in abdominal adipose tissue with weight loss. We conclude that major weight loss was associated with a late rise in serum cholesterol, possibly from mobilization of adipose cholesterol stores, which resolved when weight loss ceased.

Comments: This isn't so much about low-carb as about dieting in general. They put some people on a diet, which caused their cholesterol to go down. Then, unexpectedly, it went way up. Finally, it dropped again, and stayed there. They don't know what caused the sudden rise. The lesson? If you've been losing weight, and your cholesterol suddenly reads high, wait two months, and get it tested again.

Similar weight loss with low- or high-carbohydrate diets.

Golay A, Allaz AF, Morel Y, de Tonnac N, Tankova S, Reaven G. Department of Medicine, Geneva University Hospital, Switzerland.
Am J Clin Nutr 1996 Feb;63(2):174-178

The goal of this study was to evaluate the effect of diets that were equally low in energy but widely different in relative amounts of fat and carbohydrate on body weight during a 6-wk period of hospitalization. Consequently, 43 adult, obese persons were randomly assigned to receive diets containing 4.2 MJ/d (1000 kcal/d) composed of either 32% protein, 15% carbohydrate, and 53% fat, or 29% protein, 45% carbohydrate, and 26% fat. There was no significant difference in the amount of weight loss in response to diets containing either 15% (8.9 +/- 0.6 kg) or 45% (7.5 +/- 0.5 kg) carbohydrate. Furthermore, significant decreases in total body fat and waist-to-hip circumference were seen in both groups, and the magnitude of the changes did not vary as a function of diet composition. Fasting plasma glucose, insulin, cholesterol, and triacylglycerol concentrations decreased significantly in patients eating low-energy diets that contained 15% carbohydrate, but neither plasma insulin nor triacylglycerol concentrations fell significantly in response to the higher-carbohydrate diet. The results of this study showed that it was energy intake, not nutrient composition, that determined weight loss in response to low-energy diets over a short time period.

Comments: they got 43 people, and split them into two groups. One group got 1000 calories of low-carb food, the other group got 1000 calories of moderate-carb food. The low-carb dieters had lower cholesterol than the high-carb dieters. Notice this is backwards from the other studies. Obviously, diet doesn't have a very predictable effect on cholesterol. All you can do is try it and see.