Mainstream groups such as the American Heart Association and the American Dietetic Association endorse a unified set of dietary guidelines for people who wish to lose weight—eat a low-fat diet and cut calories.
However, many popular diet books take a very different approach. The Atkins diet, the Zone diet, Protein Power , and numerous other dietary approaches turn thumbs down on low-fat. Instead, these methods recommend cutting down on carbohydrates. According to proponents of these theories, when you reduce the carbohydrates in your diet (and, correspondingly, increase protein and/or fat), you will find it much easier to reduce your calorie intake, and you may even lose weight without cutting calories.
The controversy over these contradictions has been heated. Proponents of the low-fat diet claim that low-carbohydrate diets are ineffective and even dangerous, while low-carb proponents say much the same about the low-fat approach. However, an article published in the Journal of the American Medical Association suggests that neither side has a strong case. Researchers concluded, essentially, that a calorie is a calorie, regardless of whether it comes from a low-carbohydrate or a low-fat diet. 1 They did not find any consistent evidence that the low-carb diet makes it easier to lose weight than the low-fat diet, but neither did they find any consistent evidence for the reverse. Furthermore, the authors of the JAMA review did not find any compelling reason to conclude that low-carb diets are unsafe, although they did point out that the long-term safety of such diets remains unknown.
Subsequent studies confirmed these findings for a variety of low-carb diets.4-9,11-15,18,20-21,29 In some studies, one particular diet method may do better than others, but in other studies a different diet will stand out. Researchers reviewing 13 studies comparing low-carb against low-fat/low-calorie diets in overweight subjects for at least 6 months concluded that the low-carb diets tended to perform better at reducing weight and cardiovascular disease factors for up to one year.31 Nevertheless, a consensus has yet to emerge among nutrition scientists as to which diet performs better overall. Many of the studies cited above suggest that if a diet causes weight loss, cholesterol will improve regardless of the diet used to achieve that weight loss. However, the manner of change in cholesterol profile differs between the two approaches. Low-fat diets tend to improve total and LDL cholesterol levels, but worsen HDL and triglyceride levels, while low-carb, high fat diets have the opposite effect.22
The Mediterranean diet, which is relatively high in fiber and monounsaturated fats (eg, olive oil) has also attracted the attention of nutrition researchers. There is good evidence that it is as effective as low-carb diets for weight reduction, and probably more effective than low-fat diets.30 It also seems to have the added advantage of benefiting diabetic patients more than the other two diets.
However, if one undertakes a low-carb (or low-fat) diet that does not cause weight loss, cholesterol profile will probably not improve significantly. In addition, there is little to no evidence that the low-carb approach improves blood sugar control except insofar as it leads to weight loss. However, there is a bit of evidence that a low-carb, high-monounsaturated fat diet reduces blood pressure to a slightly greater extent than a high-carb, low-fat diet. 19 Contrary to claims by some low-carb proponents, low-fat, high-carb diets do not seem to metabolically backfire and promote weight gain. 16
Therefore, based on the current state of information, it seems that the most sensible course is as follows: If you need to lose weight, experiment with different diets, and see which one allows you to most easily cut calories (and keep them cut). If the low-carb diet approach works for you, stick with it. However, if it does not help you lose weight, you probably should not continue it indefinitely.
Note: Any form of extreme dieting can cause serious side effects or even death. We strongly recommend that all people who intend to adopt an unconventional diet should first seek medical advice. Furthermore, people with kidney failure should not use low-carb, high-protein diets, as high protein intake can easily overstress failing kidneys. (High-protein diets are probably not harmful for people with healthy kidneys. 2,3 )
In addition, people who take the blood thinner warfarin (Coumadin) may need to have their blood coagulation tested after beginning a high-protein, low-carbohydrate diet. Two case reports suggest that such diets may decrease the effectiveness of warfarin, requiring a higher dose. 10 Conversely, if you are already on warfarin and a high-protein, low-carbohydrate diet and go off the diet, you may need to reduce your warfarin dose.
2. Knight EL, Stampfer MJ, Hankinson SE, et al. The impact of protein intake on renal function decline in women with normal renal function or mild renal insufficiency. Ann Intern Med . 2003;138:460-467.
7. Pelkman CL, Fishell VK, Maddox DH, et al. Effects of moderate-fat (from monounsaturated fat) and low-fat weight-loss diets on the serum lipid profile in overweight and obese men and women. Am J Clin Nutr . 2004;79:204-212.
8. Dansinger ML, Gleason JA, Griffith JL, et al. 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.
11. Luscombe-Marsh ND, Noakes M, Wittert GA, et al. Carbohydrate-restricted diets high in either monounsaturated fat or protein are equally effective at promoting fat loss and improving blood lipids. Am J Clin Nutr. 2005;81:762-772.
12. Petersen M, Taylor MA, Saris WH, et al. Randomized, multi-center trial of two hypo-energetic diets in obese subjects: high- versus low-fat content. Int J Obes (Lond). 2005 Dec 6. [Epub ahead of print].
13. Appel LJ, Sacks FM, Carey VJ, et al. Effects of Protein, Monounsaturated Fat, and Carbohydrate Intake on Blood Pressure and Serum Lipids: Results of the OmniHeart Randomized Trial. JAMA. 2005;294:2455-2464.
14. Nordmann AJ, Nordmann A, Briel M, et al. Effects of Low-Carbohydrate vs Low-Fat Diets on Weight Loss and Cardiovascular Risk Factors: A Meta-analysis of Randomized Controlled Trials. Arch Intern Med. 2006;166:285-293.
15. Luscombe-Marsh ND, Noakes M, Wittert GA, et al. Carbohydrate-restricted diets high in either monounsaturated fat or protein are equally effective at promoting fat loss and improving blood lipids. Am J Clin Nutr. 2005;81:762-772.
17. Hodgson JM, Burke V, Beilin LJ, et al. Increased protein intake from lean red meat replacing carbohydrate-rich foods lowers blood pressure in hypertensive individuals. Asia Pac J Clin Nutr. 2005;14: Suppl:S64.
18. Gardner CD, Kiazand A, Alhassan S, et al. Comparison of the Atkins, Zone, Ornish, and LEARN diets for change in weight and related risk factors among overweight premenopausal women: the A TO Z Weight Loss Study: a randomized trial. JAMA . 2007;297:969-977.
22. Tay J, Brinkworth GD, Noakes M, et al. Metabolic effects of weight loss on a very-low-carbohydrate diet compared with an isocaloric high-carbohydrate diet in abdominally obese subjects. J Am Coll Cardiol. 2008;51:59-67.
23. Howard BV, Van Horn L, Hsia J, et al. Low-fat dietary pattern and risk of cardiovascular disease: the Women's Health Initiative Randomized Controlled Dietary Modification Trial. JAMA. 2006;295:655-666.
24. Berglund L, Lefevre M, Ginsberg HN, et al. Comparison of monounsaturated fat with carbohydrates as a replacement for saturated fat in subjects with a high metabolic risk profile: studies in the fasting and postprandial states. Am J Clin Nutr. 2007;86:1611-1620.
25. Pelkman CL, Fishell VK, Maddox DH, et al. Effects of moderate-fat (from monounsaturated fat) and low-fat weight-loss diets on the serum lipid profile in overweight and obese men and women. Am J Clin Nutr. 2004;79:204-212.
31. Hession M, Rolland C, Kulkarni U, et al. Systematic review of randomized controlled trials of low-carbohydrate vs. low-fat/low-calorie diets in the management of obesity and its comorbidities. Obes Rev. 2008 Aug 11.
Last reviewed September 2008 by EBSCO CAM Review Board
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