Low Fat vs Low Carb vs Low Cal Diets

Low Fat Diets vs. Low Carb Diets vs. Low Calorie Diets

This research was motivated by two of Gary Taube's articles Is Sugar Toxic? and What if it's all a big, fat lie?  These articles intrigued me, and I decided to try to use the tools that I use to analyze type-1 diabetes research to analyze this diet research.  If you don't like my way of discussing type-1 research, you should probably stop reading now, because you wont like this posting for all the same reasons.

This posting is divided into these sections:
  • What is the central question?
  • How will we evaluate which answer is right?
  • Discussion of each trial or research study.
  • Arguing about Studies
  • Summary and Opinions.
    • Why does it work?
    • What do I eat?
  • Studies Not Used
What is the central question?

The only thing which I think is widely agreed to in the world of diet and food, is that Americans eat too much.  The argument is about what they should focus on eating less of.  There are three common answers to this question (and thousands of uncommon ones!), and the central issue at hand is which of these is right:
  1. We should eat less calories.  It doesn't matter if we eat less fat, carbs, or proteins, what matters is that we consume fewer calories.  All calories are essentially the same (or very similar) in terms of putting on weight and general health.
  2. We should eat less fat.  Fat is particularly bad for gaining weight and overall health.  Removing 200 calories a day of fat is better for you than removing 200 calories a day of carbs or protein.  Also, this is the easiest way to lower your calorie count, so it is a two-for-one deal on diets.  (Low fat and lower calories!)
  3. We should eat less carbohydrates (called "carbs" elsewhere).  Carbohydrates are metabolized in a way which tends to make people put on weight and leads to bad health outcomes.  Removing 200 calories a day of carbs is better for you than removing 200 calories a day of fat or protein.
Obviously, there is a vast list of of things that different diets think you should eat less of , but I do not consider those, here. 

The Omnivore's Dilemma's advice is sometimes boiled down to "Eat food, not too much and mostly plants". This is mostly answer 2, since carbs are from plants while fat is mostly from animals.

How will we evaluate which answer is right?

This could be a very complex question in itself.  It boils down to the question of "what do we want in a diet?"  Different people will have different answers, but my answers (with very short justifications) are these:
  • Most important: loosing weight and keeping it off.  Most people choose a diet because they want to loose weight and keep it off.
  • Also important: good health.  The simple minded way to measure might be a measure of lifespan plus a measure of quality of life.  But that is very hard to actually do in a study.  You would need to run the study for decades to measure lifespan and people argue constantly about how to measure quality of life.  So, my measure of "good health" will be:
    • Rate of heart attack, 
    • Rate of cancer, and 
    • Rate of stroke. 
    These are all direct measures of bad health, they are the most common killers in the US, and measuring them is well understood. Unfortunately, almost no studies looked at these things, so I also included "markers" for them. By using markers rather than actual health measures, I'm opening a can of worms (does the marker accurately reflect actual health?)  but there is no way to avoid this.  Here are the markers:
    • "good" cholesterol
    • "bad" cholesterol
    • triglyserides
The heart of my method of analysis is to only look at the results of studies.  However, there is a wide range of qualities of studies.  With treatments aimed at curing type-1 diabetes, this is not an issue because almost all such trials are either very high quality or high quality.  However in the world of diet and food this is not so.  In fact, most studies are bad and many absolute crap.  So therefore, I only considered studies with the following:
  • Must be already complete and have results published in a reputable (peer reviewed and indexed) journal.
  • Must directly compare two or more of the diets above.
  • Must be prospective (not retrospective).
  • Must include at least 50 people per group, and run for at least 1 year.
  • Must include both a placebo group and a treated group, which are similar except for the treatment.
    • Assignment to groups must be random.
    • Grouping by geographical areas (especially different countries) will be excluded.
  • Must directly measure one or more of the outcomes listed above.
  • Patients must be "basically healthy", so studies done exclusively on morbidly obese people or people with type-1 or type-2 diabetes will not be included.  But overweight or moderately obese people are OK.  (That's personal for me, I started right at the border between overweight and moderately obese, so those are my peeps!)
  • Patients must not have unusual health situations, so studies done exclusively on smokers, pregnant women, etc. will not be included.
  • No study that focused narrowly on one food product or type of food product, or on one drug would be included. So studies with titles like these: "Effect of Increased Intake of Low Fat Dairy Products on Weight Loss and Insulin Resistance" or "Olestra Containing Foods and Weight Loss and Weight Maintenance" will not be included.
Some people looking at that list of exclusions and also the list of outcomes, might say "but you will ignore many valuable studies" and "what if someone does a study that shows that low fat diets lower inflammation ,which we all know is bad" or "a study without a placebo shows that you can loose 10 pounds in a week via a grapefruit only diet" or whatever it is.  My response is that I would much rather evaluate 10 really good studies, than 100 OK studies, than 1000 crummy studies.  Sure, it's always possible that one of those "extra" 90 studies will somehow be enlightening, but that's unlikely.  In a world were I have a limited amount of time, I think that spending a hour looking at each of the 10 best studies is a better use of my time than spending 6 minutes looking at each of the 100 best studies.  Plus, for me, science isn't a democracy.  It's a meritocracy.  What the 10 best studies conclude is much more important than what 100 mediocre studies conclude.

A little terminology:  Diets are often named after their creator, and diet creators spend a lot of time arguing about why their diet is different: Ornish (very low fat diet), Atkins (low carb diet), The Zone (low fat diet), LEARN (low fat diet, much like the USDA's pyramid), Mediterranean (low fat).  Generally, "low fat" means <30% of calories from fat, and "very low fat" means <10% calories from fat.

Discussion of each trial or research study
I built a list of studies to consider by searching the FDA's database on clinical trials, Google Scholar, and other on line databases.  I then reviewed several articles by Gary Taubes advocating low carbohydrate diets, and also several articles by others which advocated low fat or low calorie diets (and not low carb diets), to make sure I had all the relevant studies that either side mentioned.  Once I had the list, I discarded all studies which did not meet the criteria (above) or did not measure what I cared about (also above).  Once I realized that I had no studies that showed low-fat was better, I did specific searches to try to find any studies that showed low-fat was better and met my criteria.  The resulting studies are here.

These studies are in order best at the top to worst at the bottom.  My personal opinion on which is best, but basically: bigger, longer, younger studies are better than shorter, smaller, older ones.  You can ask my wife about that. :-)

Start: 2003  Group size: ~150 Length: 24m Diets: low carb vs. low fat
Result: no difference (low carb slightly better on non-weight results)
Results: Weight loss was approximately 11 kg (11%) at 1 year and 7 kg (7%) at 2 years. There were no differences in weight, body composition, or bone mineral density between the groups at any time point. 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.

Start: 2005  Group size: ~100 Length: 24m Diets: low-fat, Mediterranean, low-carb
Result: low carb was best
RESULTS: The mean weight loss was 2.9 kg for the low-fat group, 4.4 kg for the Mediterranean-diet group, and 4.7 kg for the low-carbohydrate group (P<0.001 for the interaction between diet group and time); among the 272 participants who completed the intervention, the mean weight losses were 3.3 kg, 4.6 kg, and 5.5 kg, respectively.
Some discussion of this study: http://lowcarbdiets.about.com/od/science/a/studynejm708.htm
Start: 2002  Group size: ~75 Diets: Atkins, Zone, LEARN, Ornish
Result: low carb is better
RESULTS:Weight loss was greater for women in the Atkins diet group compared with the other diet groups at 12 months, and mean 12-month weight loss was significantly different between the Atkins and Zone diets (P<.05). Mean 12-month weight loss was as follows: Atkins, -4.7 kg (95% confidence interval [CI], -6.3 to -3.1 kg), Zone, -1.6 kg (95% CI, -2.8 to -0.4 kg), LEARN, -2.6 kg (-3.8 to -1.3 kg), and Ornish, -2.2 kg (-3.6 to -0.8 kg). Weight loss was not statistically different among the Zone, LEARN, and Ornish groups. At 12 months, secondary outcomes for the Atkins group were comparable with or more favorable than the other diet groups.
(Technically this only lasted 48 weeks, but I rounded that to a 1 year result.)
Start: 2004  Group size: ~75 Length: 48w Diets: low carb, low fat plus drug
Result: no difference
RESULTS: Weight loss was similar for the LCKD (expected mean change, -9.5%) and the O + LFD (-8.5%) (P = .60 for comparison) groups. The LCKD had a more beneficial impact than O + LFD on systolic (-5.9 vs 1.5 mm Hg) and diastolic (-4.5 vs 0.4 mm Hg) blood pressures (P < .001 for both comparisons). High-density lipoprotein cholesterol and triglyceride levels improved similarly within both groups. Low-density lipoprotein cholesterol levels improved within the O + LFD group only, whereas glucose, insulin, and hemoglobin A(1c) levels improved within the LCKD group only; comparisons between groups, however, were not statistically significant.
Note that in this study, the low fat group, also got a drug designed to help them loose weight, while the low carb group did not.  So while this study is officially a tie, I think that it is reasonable to consider it a victory for the low carb diet.  After all, they got the same results with diet alone. 

Start: 2004  Group size: ~100 Length: 12m Diets: low glycemic load (LGL), low fat
Result: no difference
METHODS AND RESULTS: Men and women aged 30-65 years, with a BMI of 28-40 kg/m(2) (28-35 for women) and at least one criterion of metabolic syndrome were randomized to the two diets. ... The completion rate was 81%. At 3 months, weight loss was greater in the LGL group (-4.8+/-3.9 kg versus -3.8+/-3.5 kg; P=0.06) compared to the low-fat group. At 1 year, however, weight loss was similar in both groups (-4.0+/-5.5 kg versus -4.3+/-6.2 kg; n.s.), but waist circumference reduction was less in the LGL group (-3.9+/-5.3 cm versus -5.8+/-6.8 cm; P=0.03). In contrast, diastolic blood pressure decreased significantly more in the LGL group (-4.0+/-8.7 mmHg versus -1.1+/-8.5 mmHg; P=0.02). We also observed a significant interaction between the presence of the metabolic syndrome and the effect of the two diets on waist circumference, with a less favorable effect of the LGL diet in subjects without the syndrome (P=0.039).
These studies were found by using the following Clinical Trial searches:
Search Terms: low fat diet | Recruitment: Closed Studies | Study Type: Interventional Studies | Outcome Measures: weight  (total 87 studies)
Search Terms: low carbs diet | Recruitment: Closed Studies | Study Type: Interventional Studies | Outcome Measures: weight  (total 45 studies)
Search Terms: low fat diet | Recruitment: Closed Studies | Study Type: Interventional Studies | Outcome Measures: heart,cancer,stroke  (total 13 studies)
Search Terms: low carbs diet | Recruitment: Closed Studies | Study Type: Interventional Studies | Outcome Measures: heart,cancer,stroke  (total 9 studies)
and then followed with Google searches aimed specifically at trying to find a study that showed that low fat or low cal was better.

Secondary Results


Review Studies
I generally don't spend much time on review studies (studies that summarize other people's work).  Especially when I"m looking at high quality, long term diet studies, and there are so few of them.  Might was well just look at the original studies.  However, I'm including this one, because it covers studies 6 months or longer, while I only covered studies 1 year or longer.  So it's a quick and easy way to look at shorter trials, if you want to:

Summary: There are few studies comparing the effects of low-carbohydrate/high-protein diets with low-fat/high-carbohydrate diets for obesity and cardiovascular disease risk. This systematic review focuses on randomized controlled trials of low-carbohydrate diets compared with low-fat/low-calorie diets. Studies conducted in adult populations with mean or median body mass index of ≥28 kg m−2 were included. Thirteen electronic databases were searched and randomized controlled trials from January 2000 to March 2007 were evaluated. Trials were included if they lasted at least 6 months and assessed the weight-loss effects of low-carbohydrate diets against low-fat/low-calorie diets. ... Thirteen articles met the inclusion criteria. There were significant differences between the groups for weight, high-density lipoprotein cholesterol, triacylglycerols and systolic blood pressure, favouring the low-carbohydrate diet. There was a higher attrition rate in the low-fat compared with the low-carbohydrate groups suggesting a patient preference for a low-carbohydrate/high-protein approach as opposed to the Public Health preference of a low-fat/high-carbohydrate diet. Evidence from this systematic review demonstrates that low-carbohydrate/high-protein diets are more effective at 6 months and are as effective, if not more, as low-fat diets in reducing weight and cardiovascular disease risk up to 1 year. More evidence and longer-term studies are needed to assess the long-term cardiovascular benefits from the weight loss achieved using these diets.
Arguing About Studies

One of the good things about following type-1 diabetes research is that there is really very little arguing over the accuracy of studies.  That's not true about diet studies.  For diet studies, for each one published there are complaints by the people who don't agree with it's findings.  They point out problems or limitations in the study as reasons why it should be ignored.

There is no way for me to cover all the complaints about all the studies.  In any case, for me, strengths and weaknesses of studies only need to be considered in depth when there are some studies that show one thing, and some studies showing the opposite.  Then you need to look at the quality of the studies on each side.  But that's not the case here: for weight loss, there are studies showing low carb is better, and there are studies showing no difference, but no studies showing low fat (or low cal) are better.  So complaints about the details of the studies sound like wining.

Here is an article from Newsweek, and then the journal letters to the editor for the studies above:

Summary and Opinions

There are two ways to interpret these results:
  1. Three out of five studies found no difference between diets, so therefore it doesn't matter what you eat, changing your diet will not help you loose weight.
  2. Two out of five studies found low carb to be the best way to loose weight, and zero found low fat or low cal to be the best way, so if you are going to try to lose weight with diet, you should go low carb.  There is no reason to try a different diet, first.
For me, personally, I want to see 4 good solid studies before I decide the issue is closed, and we are not there yet.  However, There are 2 good solid studies showing low car diets are the best way to loose weight, and there are no studies at all saying that low fat or low cal is the best way to loose weight.  So low carb is the best option.  No other option has even one study that supports the idea that it is better than low carb.  But a few more studies confirming these results are needed to eliminate all doubt.

In doing this research, the first thing I learned was something about myself: I'm not an extremist, and a lot of the people involved in this research are.  If someone presented to me strong evidence that fat was bad, my first reaction would be to eat about 20% less fat.  If that worked well, maybe I would then lower my fat intake by an additional 20%.  But many of the researchers involved in this work think very differently.  If they think fat is bad, their first thought is "can I cut out 80% of my fat?" and if that works, "can I survive with no fat in my diet?  It's an extreme attitude that effects everything they do and think.  And I don't have it.

Why does it work / Why do you think it works?
My first answer to the question of "why does it work" is to say that "it doesn't matter".  If you loose weight, then that is enough.  Except it's not, in the real world (and especially in the world of diets).  People want to know why it works.  Here is my very brief summary.  Read Taube's articles for details:
  • In your body, calories are turned into fat only with the help of insulin.  Eat fewer carbs and your body generates less insulin and so uses your food for energy, not making fat.  Worse, insulin is good at clearing carbs out of your system and into fat quickly, so you get hungry faster.  Eat non-carbs and you body takes longer to metabolize your food, so you don't get hungry again as quickly.
  • Fructose is metabolized totally differently than sucrose (and other simple sugars).  It is metabolized by the liver, and this builds up fat around your liver, and this causes many bad effects which are not seen when you body metabolizes fat, proteins, or non-Fructose sugars.  Chief of these side effects are insulin resistance and "metabolic syndrome", which have direct impact on getting fatter and type-2 diabetes.  Finally, insulin resistance makes your body produce more insulin, with the bad effects described above.  (There is no differences between standard carbohydrates, starches, high fructose corn syrup, refined white sugar, or organic all-natural brown sugar.  They are all about 50% fructose and all identically bad, according to this theory.)
What did you eat for Lunch? / Have you lost weight?
When I blog on possible cures for type-1 diabetes no one ever asked me if took those drugs!  Yet when you write about diets, everyone wants to know if you are using it.  I don't have time or space to go into details but the answer is yes and yes.  Yes I'm using the diet (meaning my goal is to eat about 1/2 the carbs that I used to eat) and yes, I'm loosing weight.  I currently weigh less than I have in about 5 years, and I've only been on the diet a few weeks.  But the real differences is that I don't feel hungry.  I'll tell you how my cholesterol/LDL/HDL/triglyceride tests are in a year. :-)  But I'll tell you this now: for me, it is much more satisfying to eat a low carb diet, than a low fat one, much more enjoyable.

Studies Not Used

Below are a collection of studies which I did not use in my analysis.  For each study I've included why I didn't use it.  For some of them, I've included results, in case you care about them.  The most common reason (by far) was duration.  If you are willing to look at studies that are shorter than 1 year , there are a lot more to look at.  (And if you have type-2 diabetes, then you might want to focus on the three below that were done exclusively on type-2 diabetics.)

http://www.clinicaltrials.gov/ct2/show/NCT00795691 (all type-2)
Start: ??  Group size: ~50 Length: 12m Diets: low carb, low fat
Result: no difference.
RESULTS:The greatest reduction in weight and A1C occurred within the first 3 months. Weight loss occurred faster in the low-carbohydrate group than in the low-fat group (P = 0.005), but at 1 year a similar 3.4% weight reduction was seen in both dietary groups. There was no significant change in A1C in either group at 1 year. There was no change in blood pressure, but a greater increase in HDL was observed in the low-carbohydrate group (P = 0.002).
http://www.ncbi.nlm.nih.gov/pubmed/15671108?dopt=Abstract (3m)
http://www.ncbi.nlm.nih.gov/pubmed/15598683?dopt=Abstract (6m)
http://www.ncbi.nlm.nih.gov/pubmed/12679447?dopt=Abstract (6m)
http://www.clinicaltrials.gov/ct2/show/NCT00729196 (all type-2)
http://www.clinicaltrials.gov/ct2/show/NCT01029483 (6w)
http://www.clinicaltrials.gov/ct2/show/NCT00390637 (protein)
http://www.clinicaltrials.gov/ct2/show/NCT00223574 (all type-2)
http://www.clinicaltrials.gov/ct2/show/NCT00254215 (12 weeks)
http://www.clinicaltrials.gov/ct2/show/NCT00520182 (all type-2)
http://www.clinicaltrials.gov/ct2/show/NCT00351845 (36 weeks)
http://www.clinicaltrials.gov/ct2/show/NCT00324090 (10 weeks)
http://www.clinicaltrials.gov/ct2/show/NCT00422630 (6 people/group)
http://www.annals.org/content/140/10/769.short (24 weeks)
Results: A greater proportion of the low-carbohydrate diet group than the low-fat diet group completed the study (76% vs. 57%; P = 0.02). At 24 weeks, weight loss was greater in the low-carbohydrate diet group than in the low-fat diet group (mean change, −12.9% vs. −6.7%; P < 0.001). Patients in both groups lost substantially more fat mass (change, −9.4 kg with the low-carbohydrate diet vs. −4.8 kg with the low-fat diet) than fat-free mass (change, −3.3 kg vs. −2.4 kg, respectively). Compared with recipients of the low-fat diet, recipients of the low-carbohydrate diet had greater decreases in serum triglyceride levels (change, −0.84 mmol/L vs. −0.31 mmol/L [−74.2 mg/dL vs. −27.9 mg/dL]; P = 0.004) and greater increases in high-density lipoprotein cholesterol levels (0.14 mmol/L vs. −0.04 mmol/L [5.5 mg/dL vs. −1.6 mg/dL]; P < 0.001). Changes in low-density lipoprotein cholesterol level did not differ statistically (0.04 mmol/L [1.6 mg/dL] with the low-carbohydrate diet and −0.19 mmol/L [−7.4 mg/dL] with the low-fat diet; P = 0.2). Minor adverse effects were more frequent in the low-carbohydrate diet group.
http://www.annals.org/content/140/10/778.abstract (BMI>35)
Results: By 1 year, mean (±SD) weight change for persons on the low-carbohydrate diet was −5.1 ± 8.7 kg compared with −3.1 ± 8.4 kg for persons on the conventional diet. Differences between groups were not significant (−1.9 kg [95% CI, −4.9 to 1.0 kg]; P = 0.20). For persons on the low-carbohydrate diet, triglyceride levels decreased more (P = 0.044) and high-density lipoprotein cholesterol levels decreased less (P = 0.025). As seen in the small group of persons with diabetes (n = 54) and after adjustment for covariates, 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.
http://ang.sagepub.com/content/51/10/817.abstract (<15 people/group)

Future studies:


Not sure: