Studies Proving The Safety and Efficacy of the Low Carb Diet
You may have been told that low carb diets are "dangerous" and can cause heart disease. This is because for many years it was a matter of religious belief that the Low Fat diet reduced heart disease and since people with diabetes are prone to get heart disease, the assumption was that anything but a low fat diet would be dangerous for them.
This turns out to be the single most damaging non-truth ever told to people with diabetes.
$415 Million Dollars and 49,000 Women Show No Benefits to the Low Fat Diet
In 2006, The Women's Health Initiative, a $415 Million dollar, eight year study of almost 49,000 middle aged women, which had been designed to prove the health benefits of the Low Fat diet, was forced to publish these conclusions:
Over a mean of 8.1 years, a dietary intervention that reduced total fat intake and increased intakes of vegetables, fruits, and grains did not significantly reduce the risk of CHD, stroke, or CVD in postmenopausal women.
Low-Fat Dietary Pattern and Risk of Cardiovascular Disease:The Women's Health Initiative Randomized Controlled Dietary Modification Trial Barbara V. Howard et al. JAMAVol. 295 No. 6, February 8, 2006
None of the heart health claims that had been made for the Low Fat diet held up. Though diehards immediately announced that maybe further study of the Low Carb fad diet would still show results in some OTHER group, no rational person can still believe that the very high carb, Low Fat diet has any health benefits.
The same study also found that "In this study, a low-fat dietary pattern intervention did not reduce the risk of colorectal cancer in postmenopausal women during 8.1 years of follow-up." And, "Among postmenopausal women, a low-fat dietary pattern did not result in a statistically significant reduction in invasive breast cancer risk over an 8.1-year average follow-up period."
The single "positive" finding for this entire study was that the Low Fat Diet did not appear to cause significant weight gain in post-menopausal women. This sounds like good news until you realize that it didn't cause weight loss, either.
Subsequent analysis of the WHI data also found that "A low-fat dietary pattern among generally healthy postmenopausal women also showed no evidence of reducing diabetes risk after 8.1 years. This should come as no surprise to anyone who understands the basic physiological fact that the more carbohydrates you eat, the higher your blood sugar will be.
Low-Fat Dietary Pattern and Risk of Treated Diabetes Mellitus in Postmenopausal Women.The Women's Health Initiative Randomized Controlled Dietary Modification Trial.Lesley F. Tinker et al. Arch Int Med. Vol. 168 No. 14, July 28, 2008.
Studies Show That Low Carb Dieting Works and Improves Cardiac Risk Factors
Just as the health benefits of the Low Fat diet were being revealed as fantasy, a wave of good, peer reviewed studies of the Low Carb diet found that it was more effective in causing weight loss than the Low Fat diet, that it improved Triglycerides and the Framingham Cardiac Risk Ratios, and that contrary to previous belief, eating protein did not appear to damage kidneys in people who did not already have significant kidney damage.
Let's take a quick look at some of these studies.
A 2005 Comparison of Diets Shows Low Carb is Safer than Low Fat but None of the Diets Does Much for Weight
In this study,
A total of 160 participants were randomly assigned to either Atkins (carbohydrate restriction, n=40), Zone (macronutrient balance, n=40), Weight Watchers (calorie restriction, n=40), or Ornish (fat restriction, n=40) diet groups. After 2 months of maximum effort, participants selected their own levels of dietary adherence.
The group put on the Atkins diet, started out with significantly worse blood sugars than those put on the other diets, with twice as many people having abnormally high fasting glucose in this group as those in the low fat diet groups, which makes us question the way that the study was designed.
None of the groups of dieters stuck to their diets very well, and the weight loss results for all the diets were similar. However, where the low carb diet tested here made modest improvements in the subjects' HDL, triglycerides, and Framingham ratios. The ultra Low fat Ornish diet worsened cardiovascular risk factors.
Comparison of the Atkins, Ornish, Weight Watchers, and Zone Diets for Weight Loss and Heart Disease Risk Reduction. A Randomized Trial. Michael L. Dansinger, et al.JAMA. 2005;293:43-53.
A 2010 Study Finds Low Carb Diet Beats Low Fat at Improving Health Long Term
An NIH-funded study published in 2010 compared an Atkins type low carb diet to a low fat/low calorie diet over a 2 year period. This study was distinguished from earlier studies in that participants were given ongoing support to help them stay on track.
Both groups lost the same amount of weight over the two years on average. However, as stated in the results:
During the first 6 months, the low-carbohydrate diet group had greater reductions in diastolic blood pressure, triglyceride levels, and very-low-density lipoprotein cholesterol levels, lesser reductions in low-density lipoprotein cholesterol levels, and more adverse symptoms than did the low-fat diet group. The low-carbohydrate diet group had greater increases in high-density lipoprotein cholesterol levels at all time points, approximating a 23% increase at 2 years.
Though this study excluded people with diabetes, the finding confirms what people with diabetes have been reporting, anecdotally for years and removes any basis on which doctors and nutritionists can rest their oft repeated claim that the low carb diet is dangerous.
Weight and Metabolic Outcomes After 2 Years on a Low-Carbohydrate Versus Low-Fat Diet: A Randomized Trial Gary D. Foster et al. Annals of Internal Medicinevol. 153 no. 3 147-157 Aug 3, 2010.
But Hold On If You Are Female, the Low Carb DOES Beat the Others for Weight Loss
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. Christopher D. Gardner et al. JAMA. 2007;297:969-977.
This study was a "twelve-month randomized trial conducted in the United States from February 2003 to October 2005 among 311 free-living, overweight/obese (body mass index, 27-40) nondiabetic, premenopausal women."
In this study, premenopausal overweight and obese women assigned to follow the Atkins diet, which had the lowest carbohydrate intake, lost more weight and experienced more favorable overall metabolic effects at 12 months than women assigned to follow the Zone, Ornish, or LEARN diets. While questions remain about long-term effects and mechanisms, a low-carbohydrate, high-protein, high-fat diet may be considered a feasible alternative recommendation for weight loss.
You can read detailed discussions of these studies and more, as well as some others that throw light on why many people do have problems with low carb diets, in my book, Diet 101: The Truth About Low Carb Diets
A Big Meta-study Suggests Saturated Fats are Fine--Just not Trans Fat
A metastudy published in 2010 further strengthened the case that saturated fats have been unjustly demonized. It found that dairy fats appear beneficial, though the vegetable oils usually promoted by dietitians appear less so. The study can be read here:
Association of Dietary, Circulating, and Supplement Fatty Acids With Coronary Risk: A Systematic Review and Meta-analysis Rajiv Choudhury et al. Annals of Internal Medicine2014;160(6):398-406.
The study was discussed with some background information in the New York Times HERE.
One Important Warning
When I went back and carefully reread the low carb research discussed on this page while working on my new book I found some new details, and a couple longer lasting studies that pointed up an important fact that did not come out in studies that lasted a year or less.
What they have to teach us is this: Low carb diets are very healthy as long as they are really low carb. But the bad news is that if your carbohydrate intake starts to rise over 120 grams per day, your diets will become very unhealthy unless you cut back on fat. A high fat intake is only healthy with a truly low carb diet.
The studies that convinced doctors in the 1970s that low carb diets were dangerous were all studies of people eating "low carb" diets of 150 grams of carbohydrate a day or more. And more recent research suggests that those diets are just as unhealthy now as they were then.
If you can control your blood sugar with a diet that cuts carbs to a level nearer 150 grams a day, as opposed to 100 grams a day, keep your fats to 30% of all calories and you'll be fine.
What if You Have Diabetes?
Sadly, 99% of the money that is spend on "researching" diabetes goes into paying for studies sponsored by drug companies intended to come up with findings that will promote the sales of their drugs. Very little other research is done. The leadership of the American Diabetes Association, which has a stranglehold on the diabetes research community, is still hostile towards low carb diets, despite the research showing them safe and effective, which probably has a chilling effect on the choice researchers make of what to study.
A more than five years after research had made it clear that the low carb diet was safe and effective for people with diabetes, the ADA modified its 2008 Clinical Practice Recommendations to say that the evidence suggests that it is now safe for people with diabetes to eat a low carbohydrate diet for one year for weight loss purposes. But they refuse to consider the use of the low carb diet for blood sugar control, and continue to promote the low fat diet despite the lack of any evidence it does anything but worsen cardiovascular health.
Despite the lack of funding, a few researchers, headed by Dr. Yancy from Duke University, have done some work on the effects of Low Carb dieting on people diabetes.
A low-carbohydrate, ketogenic diet to treat type 2 diabetes. William S Yancy, Jr, Marjorie Foy, Allison M Chalecki, Mary C Vernon, and Eric C Westman Nutrition & Metabolism, 34doi:10.1186/1743-7075-2-34
This was a small, 16 week study of 28 participants who brought their mean A1c down from 7.5 ± 1.4% to 6.3 ± 1.0% by eating a low carbohydrate diet
The authors concluded,
LCKD [The Low Carb Ketogenic Diet] improved glycemic control in patients with type 2 diabetes such that diabetes medications were discontinued or reduced in most participants. Because the LCKD can be very effective at lowering blood glucose, patients on diabetes medication who use this diet should be under close medical supervision or capable of adjusting their medication.
Atkins Low Carb vs Low GI for 24 Weeks: Study finds Atkins Much Better for People with Diabetes
A study of people who were obese and had Type 2 diabetes compared the effect of the Atkins low carb diet--under 20grams of carbohydrate a day, vs the Low GI diet--which was 150-200 g a day for a period of 24 weeks. All participants were given strong support and ketone testing validated that the Atkins group was eating a truly ketogenic diet.
The effect of a low-carbohydrate, ketogenic diet versus a low-glycemic index diet on glycemic control in type 2 diabetes mellitus. Eric C Westman et al.Nutrition & Metabolism 2008,5:36doi:10.1186/1743-7075-5-36. December 2008.
The study found that:
Both interventions led to improvements in hemoglobin A1c, fasting glucose, fasting insulin, and weight loss. The LCKD [Atkins] group had greater improvements in hemoglobin A1c (-1.5% vs. -0.5%, p=0.03), body weight (-11.1 kg vs. -6.9 kg, p=0.008), and high density lipoprotein cholesterol (+5.6 mg/dL vs. 0 mg/dL, p<0.001) compared to the LGID [Low Glycemic] group. Diabetes medications were reduced or eliminated in 95.2% of LCKD vs. 62% of LGID participants (p<0.01).
It is significant that the group on the the Atkins diet, though they started out slightly heavier than the low GI diet group lost an average of 10 pounds more than the Low GI group.
Unfortunately, as is so often the case in diabetes studies, at the end of the study period the blood sugars of both groups were still much too high. At the start of the study, the average A1cs of the Atkins group were 8.8%. At the end they were 7.3%--the 1.5% drop cited in the quotation above.
Unfortunately, the doctors running the study appear to have encouraged the participants to stop taking diabetic medications. A 7.3% A1c is much too high to avoid complications. These people would have done much better if they had combined the very low carb diet with appropriate medications.
Other Studies of Very Small Groups Find Low Carb Diets Dramatically Reduce Diabetic Blood Sugars
Here are some earlier studies that Dr. Yancy cited in his 2005 study. Most of these involve small samples, reflecting the difficulty of getting funding for studies that will enrich no drug company.
One study of 8 men with diabetes put on a low carb diet for five weeks found,
A LoBAG [Low bioavailable Glucose--i.e. LOW CARB] diet ingested for 5 weeks dramatically reduced the circulating glucose concentration in people with untreated type 2 diabetes.
Effect of a High-Protein, Low-Carbohydrate Diet on Blood Glucose Control in People With Type 2 Diabetes. Mary C. Gannon, and Frank Q. Nuttall1, Diabetes 53:2375-2382, 2004
Another study of 10 obese men with diabetes put on a low carb diet for two weeks found,
Mean 24-hour plasma profiles of glucose levels normalized, mean hemoglobin A1c decreased from 7.3% to 6.8%, and insulin sensitivity improved by approximately 75%. Mean plasma triglyceride and cholesterol levels decreased (change, -35% and -10%, respectively)
Effect of a Low-Carbohydrate Diet on Appetite, Blood Glucose Levels, and Insulin Resistance in Obese Patients with Type 2 Diabetes. Guenther Boden, MD; Karin Sargrad, MS, RD, CDE; Carol Homko, PhD, RN, CDE; Maria Mozzoli, BS; and T. Peter Stein, PhD. Ann Intern Med. 2005 Mar 15;142(6):403-11
A Longer, Larger Study Still Finds Low Carb Diet Better for people with Diabetes Even Without Weight Loss
A longer larger study involved 132 obese adults 83% of whom had either diabetes or metabolic syndrome put half on a low carb diet and half on a "conventional weight loss diet."
The study found very slight differences in the weight loss provided by the two diets, which wasn't much, and as usual, people had difficulty staying on either diet for the year. However, the low carb diet was found to be much better for the people with diabetes.
To quote the published conclusions of this study:
As seen in the small group of persons with diabetes (n = 54) ... hemoglobin A1c levels improved more for persons on the low-carbohydrate diet. These more favorable metabolic responses to a low-carbohydrate diet remained significant after adjustment for weight loss differences. Changes in other lipids or insulin sensitivity did not differ between groups.
In short, it didn't matter whether the people with diabetes lost weight. Their blood sugars were better on the low carb diet and there was no worsening of cholesterol profiles.
The effects of low-carbohydrate versus conventional weight loss diets in severely obese adults: one-year follow-up of a randomized trial. Stern L, Iqbal N, Seshadri P, Chicano KL, Daily DA, McGrory J, Williams M, Gracely EJ, Samaha FF. Ann Intern Med. 2004 May 18;140(10):778-85.
Finally, another small Swedish study of 16 obese people with diabetes found,
After 6 months a marked reduction in bodyweight of patients in the low-carbohydrate diet group was observed, and this remained one year later.... Large changes in blood glucose levels were seen immediately.
It concludes, "A low-carbohydrate diet is an effective tool in the treatment of obese patients with type 2 diabetes."
Lasting improvement of hyperglycaemia and bodyweight: low-carbohydrate diet in type 2 diabetes. A brief report. Nielsen JV, Jönsson E, Nilsson AK. Ups J Med Sci. 2005;110(2):179-83.
Low Carbohydrate Diets and the Kidney
Many people believe that a Low Carb diet is a high protein diet, though in fact, it really is a High Fat diet. The reason it isn't correctly labeled is because of the fat phobic hysteria that gripped the medical community for several decades. But now that we know that Low Fat diets fail to live up to their health claims, perhaps we can stop fearing the word "Fat" and tell the truth about what the Low Carb diet really is.
A healthy low carb diet should have enough protein in it to provide the protein you need to maintain your muscle tissue. If you are eating a very low carb diet, you need to eat enough protein to let the liver turn that protein into the carbohydrate you need to run your brain. A calculator using the latest formulas used to come up with how much fat and protein you need to eat depending on carb intake, your size, and your activity level is found HERE.
However, if you are concerned that there might be dangers in eating this moderate protein intake, you should know that a large study of 1624 women in the Nurses Health Study has found that a high protein is not dangerous unless you already have kidney damage.
The authors of this study reported:
We observed no significant adverse renal effects of high protein consumption in women who had normal renal function at baseline. In addition, when we separately analyzed nondairy animal, dairy, and vegetable protein intake, we found no evidence of a detrimental effect of animal protein compared with vegetable protein.
However, they also note "We were also interested in the impact of dietary protein consumption in women with mild renal insufficiency. When we separately examined these women, we found that those who consumed the most protein had the greatest decline in estimated GFR."
This means that if you already have kidney damage you should replace most of your dietary carbohydrates with fats, rather than protein. However, it is worth noting that this study was one where high protein was being eaten in the presence of a high carbohydrate intake.
The Impact of Protein Intake on Renal Function Decline in Women with Normal Renal Function or Mild Renal Insufficiency. Eric L. Knight, MD, MPH; Meir J. Stampfer, MD, DrPH; Susan E. Hankinson, RN, ScD; Donna Spiegelman, ScD; and Gary C. Curhan, MD, ScD.Annals of Internal Medicine. 18 March 2003.Volume 138 Issue 6. Pages 460-467
There is some anecdotal evidence that a very low carb diet with adequate protein is safe for people with early diabetic kidney disease. Dr. Bernstein discusses this topic at length in his book, Dr. Bernstein's Diabetes Solution.
There does not seem to be any study that examines the impact of a moderate protein diet combined with very low carbohydrate intake on the kidney function of people with diabetes.
Low Carb Diet and the Brain
This study published in 2007 compared a Low Carb diet with a High Carb/Low fat diet. It studied 93 overweight or obese subjects (not diabetic) who ate a ketogenic diet for eight weeks.
The study concluded,
The LCHF diet resulted in significantly greater weight loss than did the HCLF diet (7.8 ± 0.4 and 6.4 ± 0.4 kg, respectively; P = 0.04). Both groups showed improvements in psychological well-being (P < 0.01 for time), with the greatest effect occurring during the first 2 wk, but there was no significant difference between groups. There were no significant between-group differences in working memory (P = 0.68), but there was a significant time x diet interaction for speed of processing (P = 0.04), so that this measure improved less in the LCHF than in the HCLF diet group.
In short, eating well below the 130 grams of carbs ignorant dietitians will tell you are essential for brain function works fine. Memory was not affected, and mood improved. Speed of processing "improved less" than it did on a low fat diet in this group. However, this may be because of the elevated blood sugar caused by the Low Fat diet. Over time, the damage caused by higher blood sugars to the brain, and the known association of high blood sugar with dementia would outweigh this very minor difference.
Note, also that the speed of processing of those eating the low carbohydrate diet did not decrease relative to baseline.
Low- and high-carbohydrate weight-loss diets have similar effects on mood but not cognitive performance. Angela K Halyburton, Grant D Brinkworth, Carlene J Wilson, Manny Noakes, Jonathan D Buckley, Jennifer B Keogh and Peter M Clifton. American Journal of Clinical Nutrition, Vol. 86, No. 3, 580-587, September 2007.
The 10,000 Pound Gorilla of Nutritional Research: Gary Taubes' Book Good Calories, Bad Calories
If you are really interested in learning the whole ugly history of why modern nutritional "science" has endorsed the low fat diet hypothesis in the absence of any rigorous research supporting its effectiveness either for fighting heart disease or causing weight loss, you must read Gary Taubes' book, published in October of 2007, Good Calories, Bad Calories. Taubes provides descriptions and analyses of hundreds of nutritional studies performed since the 1940s. He also cites several well-conducted studies whose results were suppressed because they didn't match what diet authorities thought the results should be. Taubes also shows how many studies that have been cited over the years to support the low fat hypothesis actually did not prove what they were said to prove.
While many reviewers have quibbled with a sentence here or there in Taubes' book, there is no way a thinking person can read it and not end up agreeing with is main point which is that mainstream diet advice over the past fifty years has not been based on the findings of well conducted scientific research, for reasons that have to do with the way personality and power politics play out within the scientific community.
A Final Caution About "Low Carb" Diet Studies
You will see a lot of studies, often published in prestigious journals, that claim to prove that some other diet is better for people with diabetes than a low carb diet. Before you get swayed by these findings, take a close look at the study and see how the researchers define "low carbohydrate."
In quite a few high profile studies published recently the "low carb" diet turns out to be one containing anywhere from 120 to 180 grams of carbohydrate a day. For most of us, this is far too much carbohydrate. It will raise our blood sugar dramatically and when that happens, we lose all the benefits of carb restriction.
Be Skeptical of Scare Studies
The evidence in support of the efficacy and safety of low carb diets keeps accumulating. But there is a lot of money in selling cheap grains to people with cardiovascular disease and diabetes and calling these cheap grains "health food".
The big health organizations like the American Heart Association and the American Diabetes Association have spent decades telling the public that eating fat is dangerous and that high carbohydrate diets are healthy. They continue to do so rather than admit that for a generation they've been giving the public flawed advice that worsens their diabetes and heart disease.
As a result, you see a persistent stream of studies that are presented as if they proved that eating a low carb diet will give you a heart attack. When the press reports on these studies reporters invariably add that eating a low fat diet will prevent heart disease--though as you read above, huge studies lasting many years and involving many thousands of humans have been unable to come up with any data to support this theory.
When studies attacking low carb diets involve human subjects, they often draw their conclusions from the analysis of food questionnaires. An example are studies that claim that eating meat leads to terrible health outcomes. What these studies don't do, is ask people what they ate with their meat, which is often supersized fries, soda, and a huge, sugary dessert.
They also don't ask them what exactly they meant by "meat." Pink slime burgers infused with a cocktail of powerful chemicals, including damaging inorganic phosphates and MSG, consumed at fast food outlets, are very different in their nutritional impact than organic meats or artisanal cheeses served with fresh vegetables. Cutting carbs does not make chemical-laced low quality food healthy, so if you cut your carbs, do what you can to improve the quality of the foods you eat.
The Standardized Nutritional Questionnaire Isn't Accurate when People Eat Low Carb Diets
Beyond that, the questionnaire used in these studies is constructed so that it is not able to identify people eating real world low carb diets. Years ago I embarked on a year long quest to understand how food interacted with my body. At the time I was eating on average 65 g of carbs a day. For several months I weighed almost all of my portions on a food scale and used very accurate nutritional software that let me enter in all the recipes I used to record exactly what I had eaten. My software was able to tell me exactly what proportion of fat, carbs, and protein I had eaten, along with a lot of other information.
At the same time I was a subject in a low carb diet research project which used the standardized nutritional questionnaire. I filled it out as accurately as possible, and the chief researcher sent me the nutritional breakdown that her software had calculated from my questionnaire. The numbers she reported to me bore NO relationship to what my logging had found. It showed me as eating far more carbs than I actually was eating and a lot more protein. When I offered to send in my logs, I was politely turned down.
But this tells me that anyone who can looks like they aren't eating carbs on these questionnaires must be eating a very extreme diet.
The most common scare studies you will see reported in the press are conducted in rodents and involved some bizarre study designs. Scientists create genetically engineered mice carrying genes that make them unable to metabolize fat properly and then feed them fat. They feed mice a lot of fructose along with their "high fat" diet but neglect to mention the fructose when describing the toxic effect of the "high fat" diet though there is quite a bit of evidence that fructose promotes heart disease independent of fat intake. They may feed animals shortening filled with cardio-toxic trans fats and then find that these trans fats have clogged the animals' arteries. Trans fat does this whether or not you eat it with or without carbs, though you are more likely to encounter trans fat in high carb packaged foods and in foods like fast food french fries or coffee shop pastry.
Sometimes the scientists feed animals extremely high protein diets--which are quite different from the high fat diet that the low carb dieter eats. The proteins they choose are filled with high levels of minerals mice don't have the kidney's to metabolize. This leads to severe disease, but again, has nothing to do with the low carb diet and nothing to do with humans, either. Human kidneys are evolved to work well with a meat based diet. Mice you may remember are not carnivores.
To read a brilliant analysis of how flawed animal studies are that connect dietary fat with heart disease read this blog post by Dr. Stephan Guyanet:
If you have a concern about the safety of your low carb diet, you might want to have a look at the list of safety guidelines I have posted on our low carb diet sister site. You'll find it here: Is Your Low Carb Diet Safe?