September/October 2004

What's the beef? 
The downside of the low-carb diet

By Ravi Dykema

 

      Can a meat-heavy diet really be good for us? Here, Amy Joy Lanou, Ph.D., nutrition director of the Physician's Committee for Responsible Medicine, talks about the downside of too much protein.

RD: What are some of the main concerns about a low-carb diet?

AL : There's certainly no contention that low-carbohydrate, high-protein diets do help some people lose weight. Some people do experience dramatic weight loss. However, when you actually look at the controlled trials, they're similar to other diets in terms of the amount of weight loss-about a pound a week for the first few months, then less over time. Just like you might see with a calorie-restricted diet or a high-carb diet or any other weight loss plan.

      And there are some real health concerns related to using low-carbohydrate, high-protein diets for weight loss. They range from sudden death to constipation. We've seen a lot of cases of cardiac arrhythmias. We've seen people who have gone from having apparently clean arteries to needing a stint placement in a year or two on these diets. People have experienced reduced kidney function, kidney stones, gout, gall bladder problems-the list of different problems is long, but those are the best documented.

 

RD: Michael Eades [see interview] says that, as a species, we've evolved to do best on a low-carb diet. Any thoughts on that?

AL : I am definitely not an expert on prehistoric man, but I do know that life spans have been getting longer, and some of the health concerns we see now weren't apparent at all in populations that died in their 30s and 40s. We're living into our 70s, 80s and 90s now, sometimes even longer. Additionally, we're far less active than most of our ancestors. So a diet that may have been appropriate for a very active, young body does not seem to be the best for a longer-living, more sedentary human population. Many people around the world live well into their 90s and 100s on very high-carbohydrate, low-fat diets with modest protein.

 

We've seen people who have gone from having apparently clean arteries to needing a stint placement in a year or two on low-carb diets. Many people around the world live well into their 90s and 100s on very high-carbohydrate, low-fat diets with modest protein. A food-pyramid diet isn't the healthiest way to eat. It's just the federal government's compromise between what the science says and what corporate America is willing to put up with. No studies longer than a year have looked at the effect of a low-carbohydrate, high-protein diet on weight loss, or any other effects in the body. Many of our health problems have less to do with macro-nutrients and more to do with the kind of processing food has undergone between when it was raised and when we eat it.

RD: Do you think, as a species, that we're herbivores?

AL : From a biologic perspective, we're omnivores. We're not carnivores, and we're probably not herbivores. We clearly can digest meat. We can chew. We have the right teeth for it. But, although we can chew meat and our bodies can digest it, I think that most people live healthier and longer when they choose a diet that has either limited or no meat.

 

RD: What about essential nutrients, like vitamin B12, that we can get only from animal products?

AL : It is true that our bodies need vitamin B12, and people who eat absolutely no animal products need to supplement with vitamin B12.  But you only need a little bit, every so often. You certainly don't need a diet that's mostly meat or even a third meat. And dairy products do contain vitamin B12.

 

RD: But doesn't most new research support a low-carb diet?

AL : It depends on what you're looking at. In some ways, I totally agree with Michael Eades and some of the low-carb proponents. I get frustrated when they make erroneous comparisons. For example, some recent studies in the New England Journal of Medicine have compared low-carb, high-protein diets to a food-pyramid eating pattern. But a food-pyramid eating pattern is not what I would consider the healthiest way to eat. It's just the federal government's compromise between what the science says and what corporate America -feed and dairy industries, and other manufacturing industries-are willing to put up with. We need more studies that look at truly good diets, rather than comparing the low-carb diet to this compromise mish-mash that's just slightly better than the standard American diet.

      Another problem I have is that the studies on low-carb diets haven't looked at long-term effects of that diet. As far as I know, there are no studies longer than a year that have looked at the effect of a low-carbohydrate, high-protein diet on weight loss, or any other effects in the body. We know diets that are too high in protein cause certain problems. We know that diets that are too high in saturated fats cause other problems. But we really don't know enough about the long-term effects of that combination of high protein and high fat. 

      However, we do know a good bit about the long-term effects of a diet that's high in plant foods. We know that low-fat diets rich in whole plant foods do have really beneficial effects over the long term. I think it would be really useful to compare those two diets-a low-carb diet and a plant-based, low-fat diet-using a standard American diet as a control.

 

RD: What are some of the benefits of a diet that's high in plant food?

AL : We know we can reverse heart disease with a plant-based, low-fat diet. We know if you put people on a low-fat, plant-based diet, they'll lose weight. We're currently doing a study of people with type 2 diabetes, and we're showing that they're becoming non-diabetics on this diet. I know lots of people are having pretty scary problems on a low-carb diet, and I know lots of people are succeeding on them. But as far as long-term benefits go, I don't think there's enough evidence. I don't feel like it would be ethical to put people on a Protein Power diet or Atkins diet.

 

"We've seen people who have gone from having apparently clean arteries to needing a stint placement in a year or two on low-carb diets."

RD: What would make it unethical?

AL : For me, the concerns about possible problems with cardiac arrhythmia or atherosclerosis. It's just a little too scary for me.

 

RD: What is it about the low-carb diet that you think causes arrhythmia?

AL : It likely has to do with getting acid balance and fluids and electrolytes out of whack. On a high protein, low-carb diet, the body has to process more metabolic acids. In order to neutralize those acids and clear them out, the body uses minerals, including calcium and potassium. Potassium is really important for electrolyte balance. When electrolytes get out of balance, the heart can misfire.

      Another problem with low-carb diets is the lack of fiber. In the induction phase of some of these diets-the phase where carbs are severely restricted-times in that period, people will experience constipation. We have a registry on our website (www.pcrm.org) where people can tell us about issues they've had with their diets. Some people on high protein, low-carb diets have said they didn't defecate for 14 days-the lack of fiber on the diet caused really horrific constipation. Then people may take a laxative, and further exacerbate their electrolyte balance problems, because laxatives make you lose minerals from the body as well. Of course, it depends on the composition of the low-carb diet. When the diet is high in animal foods, it is often lower in plant foods and, thus, lower in fiber.

 

RD: Some studies have shown that low-carb or low-calorie diets-which probably reduce carbs-help improve insulin resistance.

AL : Yes, and there's a third way-that is to use an almost all plant food diet that's very low in fat and very high in carbs. We've done clinical trials with diabetics, and we've seen improved insulin resistance in women on a low-fat vegan diet for 11 weeks. I think the key is that both a plant-based, low-fat diet and a well-planned low-carb diet avoid highly processed foods, like cakes, cookies, chips, soda and so on.

      It sounds like the Eades would recommend that people avoid grains and look at whole plant foods and whole animal foods-I'm sure they're not recommending hot dogs and bologna and those kinds of things. This is a commonality in our approach: Many of our health problems have less to do with macro-nutrients-carbs, protein and fat-and more to do with the kind of processing food has undergone between when it was raised and when we eat it.

      When whole foods are processed, they lose nutritious substances that we need for health-vitamins, minerals and fiber-and they often gain (or concentrate) substances that we want to limit for health reasons, like fat, salt and sugar. Compare a whole potato to a bag of potato chips or whole wheat to Fruit Loops. In addition, with regards to insulin resistance, when foods are processed, fiber is reduced or taken out and the carbohydrate source is modified (as in wheat flour to white flour); this changes the way the insulin-glucagon hormonal system responds to the ingestion of the food. When foods are more processed, they tend to have a higher glycemic index, which means that the rate at which blood sugar rises after consuming them is higher.

 

RD: I see. It also appears that lipids and triglycerides also improved on a low-carb diet.

AL : It is true that people on these low-carb, high-protein diets generally see some drops in those markers. The place where things get a little messy is with cholesterol. If you look at the studies, a proportion of people on these diets do seem to show a drop in cholesterol. That may be because they're losing weight. However, about a third of people in these studies show pretty dramatic increases in cholesterol levels, so it's not a universal effect. In fact, some studies have had a number of people drop out because their cholesterol shot so high. I wouldn't argue that a low-carb diet can cause some drops in cholesterol, but it's not a universal effect.

 

RD: But isn't the ratio between LDL and HDL levels more important than total cholesterol? I thought many studies showed that the increase in HDL ("good") cholesterol on a low-carb diet would compensate for any slight increase in LDL ("bad") cholesterol.

AL : I haven't seen any data that shows that. I'd certainly be interested in seeing it, but I haven't seen any that convinces me that that's the case.

 

"Many people around  the world live well into their 90s and 100s in very high-carbohydrate, low-fat diets with modest protein."

RD: In a recent edition of Science News, there's an argument about the pros and cons of the low-carb diet that cites a couple of studies showing a positive benefit on LDL/HDL ratio on a low-carb diet. It also sites a study in which one person pulled out because of a spike in his LDL, but the rest of the participants stayed in the study. It sounds like you're interpreting the study data differently than Michael Eades is.

AL : I don't think there's any conclusive evidence that low-carbohydrate, high-protein diets are safe, and I certainly don't think there's conclusive evidence that they are beneficial for reducing chronic disease risk.

 

RD: What about some of the other purported benefits of a low-carb diet, like reducing sleep apnea, treating gastroesphagel reflux syndrome and lowering blood pressure?

AL : Any diet that lowers weight will also help with these conditions. I am not aware of any published evidence for these specific conditions.

 

RD: What about the argument that a low-carb, high-protein diet stresses the kidneys?

AL : There are two lines of response to that. First, the American Kidney Fund has a position statement specifically against high-protein diets, because of their negative effects on the kidneys. I would also agree that rampant, uncontrolled glucose levels-like you might find on a high-sugar, standard American diet-is hard on the kidneys as well. 

"No studies longer than a year have looked at the effect of a low-carbohydrate diet on weight loss, or any other effects in the body."

      One recent study showed that if a person has somewhat reduced kidney function, being on a high-protein diet will further reduce kidney function, or increase kidney problems. Now, that's only if a person already has some reduction in kidney function. Another study shows that one in four American adults has marginally reduced kidney function, so it wouldn't be unlikely for one out of four people on a low-carb, high-protein diet to have some stress on their kidneys.

      An abundance of protein and the state of ketotis that's encouraged by many of these diets does make the kidneys work harder. If you have perfectly healthy kidneys, they can work harder 'til the cows come home. But if you have some reduced kidney function, then you are potentially putting your kidneys at risk. 

The carb controversy: The truth about the low-carb diet