Low-Carb vs. Low-Fat — What Does Research Show?
Saturday, July 7, 2012
LifeTime WeightLoss in Low-Carb, Nutrition, Tom Nikkola, low-fat

The use of a reduced-carbohydrate diet is surrounded in myth and misunderstanding. Though carbohydrate reduction has been used in practice for more than a couple centuries, only over the past 50 to 60 years has it come under attack as being ineffective or even unhealthy. From personal experience, I know that even many supposed experts in health and fitness perpetuate false information about “going low-carb.”

To satisfy some curiosity as well as to put together a resource I can refer back to when needed, I summarized 14 random, controlled diet trials that compared reduced-carbohydrate diets to low-fat diets. You can download the PDF of the table I created by clicking on the image below. If you'd prefer to just read about the highlights, read on below.


What is special about these studies? As mentioned, they’re random, controlled trials. This means different groups were assigned different diets and resources to help them adhere to the recommended nutrition plan. Of course, there is human error and, in most cases, study participants had freedom to veer off their expected plan. However, when you take such a large number of studies and understand the consistent results they deliver, you see some very consistent effects of lowering carbohydrate intake compared to standard “heart-healthy” low-fat recommendations.

If you tend to keep an eye on media headlines, keep in mind that most studies that make the news are observational studies. They look at a large population and see what trends exist. For example, a 25-year study from Sweden recently made headlines such as “Time to Retire the Low-Carb Diet Fad.” If you just read the headline, you got the impression low-carb doesn’t work, and the impression that it is just a fad (that’s been around for a couple hundred years). As is often the case, this study was observational. I’ll review the study and share the facts surrounding it at some point, but if a friends tells you about it, don’t worry about it.

Are reduced-carbohydrate diets effective for weight loss?

Let’s face it. Obesity is an enormous problem. The population of most of the world, especially the Western world, is fat. Take a look around at the mall, the airport or your state fair the next time you have the chance. If there is a better solution to help get peoples’ bodies back to healthy levels of body fat than carbohydrate restriction, research hasn’t shown it yet. In fact, when you look at the results of the lower-carb diets, even when people are free to eat as much as they’d like, they are far superior in terms of weight loss to calorie-controlled, low-fat diets.

If you were to read through many of the low-carb studies, you’d see the study participants often do not adhere to the exact levels of carbohydrate intake they’re supposed to. However, it’s still much lower than the low-fat comparison group, which is closer to the Standard American Diet. In most studies, weight loss and fat mass loss are close to double that of the results from low-fat diets. Again, in most studies, participants are instructed to keep carbohydrate to a maximum amount, often 20 to 50 grams to start. They’re then told they can eat as much food as they like, as long as they don’t exceed the 20 to 50 grams of carbohydrate.

The comparison group, the low-fat group, is often given an exact amount of calories they’re allowed each day. The calorie level is intended to force them into a calorie deficit to ensure weight loss.

Think about it. Which is more appealing? To follow a calorie-controlled diet where foods should be weighed and measured each day to ensure you don’t overeat, or follow a diet where you can eat as much as you’d like of most foods, other than starches, and get the added bonus of greater weight loss? In the research, those following the lower-carb diets often eat fewer calories than those following the low-fat, calorie-controlled diets, but it’s by choice. No weighing or measuring is required. They just eat until they’re satisfied, and become satisfied faster because they’re not eating such large amounts of carbohydrate, and also getting more hunger-reducing fat in the diet.

Do reduced-carbohydrate diets increase the risk of heart disease?

I often smile when people bring this up as a reason not to try lower-carbohydrate diets. For some people, you can give them all the proof in the world that lower-carb diets result in far greater weight loss, but because they may not want to acknowledge their effectiveness, they proclaim the heart disease risk the diets cause.

In the context of high- and low-carbohydrate diets, heart disease risk is often determined based on blood levels of LDL cholesterol, HDL cholesterol, triglycerides and glucose. If a diet negatively impacts lipid and glucose levels, it may increase the risk of developing heart disease. Being overweight also increases the risk of developing heart disease, so the fact that low-carbohydrate diets have been shown to be more effective for weight loss suggests they can also improve future health outcomes.

Even so, some people point at lipid levels and suggest that the added fat in the diet will cause problems. In an ideal world, according to conventional thought, a diet should lower LDL cholesterol, raise HDL cholesterol, lower triglycerides and lower glucose levels. Many see the value of the ratio of LDL and HDL as superior to looking at the numbers alone, so if a diet were to equally increase LDL and HDL by similar levels, it would actually improve the LDL/HDL ratio and lower risk.

In addition, those following lower-carbohydrate diets often end up with lower actual LDL particle numbers, a much more predictive measure of heart disease risk, even though the concentration of cholesterol may be higher. Peter Attia has been writing an excellent series of articles on this topic if you’d like more information: The Straight Dope on Cholesterol.

Again, considering the research, how does low-carb compare to low-fat when it comes to lipids and glucose?

In almost every case, HDL cholesterol levels increase in a low-carb diet, far more than from a low-fat diet. In fact, some studies show HDL cholesterol drops on a low-fat diet. HDL cholesterol is seen as protective and, for the most part, the more you have, the better. Saturated fat tends to support higher HDL cholesterol the most from a diet standpoint.

Most times, a slight increase in LDL cholesterol is seen with low-carb, and a reduction is seen with low-fat. However, lower LDL cholesterol by itself is not always good. If the concentration of LDL cholesterol goes down but the number of LDL particles in the blood goes up, it can increase the risk of heart disease.

Triglycerides are another marker to be aware of. Unfortunately, cholesterol gets the bulk of the attention, but elevated triglyceride levels are no less important than understanding cholesterol levels. In fact, comparing triglycerides against HDL (trig/HDL ratio) may be even more predictive of heart disease risk than LDL and HDL comparisons. For triglyceride levels, studies show a dramatic decrease in levels with the use of a low-carbohydrate diet. Carbohydrate consumption increases the production of triglycerides, so lowering carbohydrate levels has a major impact. In some of the studies, triglyceride levels actually went up as a result of following a low-fat diet. If they did go down, the reduction was often unimpressive compared to those on the low-carb diets.

Researchers from the diet trials summarized their findings with conclusions such as:

"The more favorable effects on lipids (with the low-carbohydrate diet) and on glycemic control (with the Mediterranean diet) suggest that personal preferences and metabolic considerations might inform individualized tailoring of dietary interventions.”" (1)

"Severely obese subjects with a high prevalence of diabetes or the metabolic syndrome lost more weight during six months on a carbohydrate-restricted diet than on a calorie- and fat-restricted diet, with a relative improvement in insulin sensitivity and triglyceride levels."” (3)

"Compared with a low-fat diet, a low-carbohydrate diet program had better participant retention and greater weight loss. During active weight loss, serum triglyceride levels decreased more and high-density lipoprotein cholesterol levels increased more with the low-carbohydrate diet than with the low-fat diet."” (5)

"The LC diet appears to be an effective method for short-term weight loss in overweight adolescents and does not harm the lipid profile.”"(6)

"...a very low carbohydrate diet is more effective than a low fat diet for short-term weight loss and, over 6 months, is not associated with deleterious effects on important cardiovascular risk factors in healthy women."” (7)

"Despite a threefold higher intake of dietary saturated fat during the CRD, saturated fatty acids in TAG and cholesteryl ester were significantly decreased, as was palmitoleic acid (16:1n-7), an endogenous marker of lipogenesis, compared to subjects consuming the LFD...The results support the use of dietary carbohydrate restriction as an effective approach to improve features of MetS (metabolic syndrome) and cardiovascular risk."” (8)

Are reduced-carbohydrate diets effective for managing blood sugar?

Blood glucose levels are heavily influenced by the amount of carbohydrates in the diet, so it’s no surprise that in the studies comparing low-carb and low-fat diets where glucose was measured, low-carb did better than low-fat at lowering blood glucose levels, sometimes dramatically better. One study also included the use of a Mediterranean diet, and the Mediterranean diet did better than low-carb or low-fat at lowering glucose levels, though low-carb was still superior for improving lipid profiles and weight loss. In fact, when diabetic patients follow a low-carb diet, the drop in blood glucose is even more significant than when those who have normal glucose levels use low-carb. Knowing what research suggests, it’s surprising the American Diabetes Association still recommends a high-carb, low-fat diet. The free meal plan generator on their site came up with a recommended meal plan of 1610 calories, 205 grams of carbs, 88 grams of protein and 55 grams of fat (~50% carb, 20% protein, 30% fat).

Are reduced-carbohydrate diets easier to maintain than calorie-restricted, low-fat diets?

If reduced-carbohydrate diets are more effective for weight loss, improving lipid profiles and managing blood sugar, what about the ability for people to stick with them? Even if they’re effective, they’re only effective when people follow them. The bigger question should be “Are low-carb diets more difficult to sustain than other diets?” According to many of the papers referenced above, those in research studies adhere to low-carb about as well as other diets.

Does that mean they’re easy? Not when people still have carbohydrate-rich processed foods in the house. If someone is to be successful long term, he or she must make a commitment to stay away from the foods that negatively impact their health. That would be the case no matter what type of “diet” individuals eat. However, the reason people are able to more easily fit a lower-carb diet into their lifestyles is that it doesn’t require calorie-counting, starvation or any other issues common with low-calorie, low-fat diets.

The majority of studies on low-fat diets versus low-carb compare a calorie-restricted, low-fat diet against a low-carb, ad libitum (eat as much as you wish) diet. Often, people actually eat fewer calories on the low-carb diet without thinking about it because they’re more satisfied. The bottom line is, according to the evidence, if people wish to change their lifestyle, a reduced-carb approach to eating is much easier to adapt than the low-fat alternative. As the researchers in the Journal of the American Dietetic Association concluded:

"This perception of less hunger and equivalent restraint with a low-carbohydrate/high-protein diet may explain the greater BW loss compared with the high-carbohydrate/low-fat diet."” (15)

Is carbohydrate reduction appropriate for kids?

With the alarming rates of overweight and obesekids, two studies offer some fascinating feedback. Both studies come from The Journal of Pediatrics. In one 12-week study, a group of adolescents were split into two groups. One group was put on a low-fat, low-calorie diet where their daily calorie target was 30% lower than their maintenance level. The other group was put on a diet that limited carbohydrate intake to 20 grams, targeted protein at about a gram per pound of target body weight, and allowed for unlimited total calorie intake. This is key, as it is in many of the other low-carb studies; the low-carb group doesn’t have a calorie limit. In this study, the low-carb group lost an average of 29 pounds compared to the low-fat group that lost just 16 pounds! The low-carb group also had a dramatic drop in triglyceride levels.

The second study was designed with similar nutrition targets and also lasted 12 weeks. The low-carb group lost more than twice as much weight in 12 weeks and also saw a tremendous drop in triglycerides.

Most parents are told their kids need to exercise more and eat less. These two studies beg for a different approach to help control the rates of obesity in youth.

How much carbohydrate is acceptable?

The final question is a personal one: “How much carbohydrate is right for me?” At Life Time, the breakdown of macronutrients for the average person is around 40% carbohydrate, 30% protein and 30% fat. There is nothing magical about these macronutrient levels, other than the fact that they are lower in carbohydrate and higher in protein than the Standard American Diet. It’s a starting point. Someone eating 2000 calories a day would get 200 grams of carbohydrate.

Based on the research, that’s a LOT of carbohydrate and much more than most people would need. However, it’s less than the general population gets. Looking at the research comparing low-fat and low-carb, most of the studies start people with 20 grams of carbohydrates per day, which is what Dr. Atkins encouraged beginning with his first book. However, the misconception is that people should stay there and that is not the case. The method many of the research studies used was to start people at 20 grams or less per day for the first couple weeks and then add in 5 grams more of carbohydrate per day each week. Carbohydrates would continue to be added into the diet until weight loss slowed or other indicators showed that the individual was getting too much carbohydrate.

Though some people with insulin resistance or carbohydrate intolerance should maintain a very-low carbohydrate diet, it is not necessary for most people. It also should not be done without an experienced health care professional’s support, especially for those on glucose-lowering medications.

So is there an ideal range? It’s hard to say at this point. Less than 150 grams a day for most people is likely appropriate. Many find their sweet spot to be between 50 to 100 grams per day. Though people are free to experiment with their diet as they see fit, I would strongly encourage those who are considering a reduced-carbohydrate diet to work with a dietitian.

The approach to modifying your diet depends on your starting point, your current health status, and the appropriate approach for making changes. In our experience, the faster one jumps into a new nutrition plan, the easier it is for them to jump back out of it. In the end, we’re not talking about reducing carbohydrate intake as a way to diet. We’re looking at it as a lifestyle. The goal is to make it something that can be maintained for the rest of your life, so you can maintain the improved lipid profiles, the healthy weight, better energy and lack of focus on dieting. By working with a nutrition professional, you can focus on manageable steps each week to make this a new way of living. After all, if your health improves, the weight starts to come off anyway.


Random, controlled trials are considered the best way to determine what people should be doing to optimize their health and manage weight. Low-carb diets have a reputation for being only as effective as low-fat diets in weight loss and for increasing the risk of developing heart disease. The random, controlled trials suggest otherwise. As we face the burden of growing health care costs and a decreasing quality of life from our growing waistlines and declining health, we must look at what the evidence suggests based on studies such as these rather than repeating the dietary advice that is conventional or popular.  

Written By Tom Nikkola - Director of Nutrition and Weight Management

This article is not intended for the treatment or prevention of disease, nor as a substitute for medical treatment, nor as an alternative to medical advice. Use of recommendations in this and other articles is at the choice and risk of the reader.

Article originally appeared on LifeTime WeightLoss (http://www.lifetime-weightloss.com/).
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