Carbohydrate Restriction: The Numbers Don’t Lie

I love intelligently designed research. But what I love even more are intelligently designed research studies that are carried out long enough to provide us serious insight into human health and performance.

One of the best studies on diet effectiveness ever published (in my opinion at least) came out in 2008 in the New England Journal of Medicine. This study1, which followed 322 obese adults for 2 years, looked at the impact of a low-fat diet vs. the Mediterranean diet vs. a low-carb diet on weight loss.

The beauty of this study was two-fold:

  1. It ran for two years, which is long enough for true diet difference to emerge.
  2. It was conducted on moderately obese individuals (BMI of 31), not individuals with a diagnosed metabolic disorder (e.g. diabetes).

The fact that the study ran 2-years eliminated one of the most common problems with diet studies: that most participants are quite compliant when followed closely by a researcher. However as time goes on, excitement and compliance wane, making a 2-year investigation quite telling at the end of the day.

The diets themselves were patterned off popular diets:

Low-Fat (based on American Heart Association guidelines)

Calorie goal: 1500 kcal females, 1800 kcal males
Total fat: < 30% of calories
Saturated fat: < 10% of calories
Cholesterol: < 300 mg/day
The participants were counseled to consume low-fat grains, vegetables, fruits, and legumes and to limit their consumption of additional fats, sweets, and high-fat snacks.

Incidentally, the nutrition principles being taught in medical schools and to dietitians in North America are basically an extension of the low-fat diet principles.

Mediterranean Diet

Calorie goal: 1500 kcal females, 1800 kcal males
Total fat: < 35% of calories
Added fats came from olive oil and nuts
The participants were counseled to decrease their intake of red meat and increase their intake of poultry and fish.

Low-Carb (based on Atkins)

No calorie limit
Carbohydrate goal: 20 g/day for 2-months, then up to a maximum of 120 g/day
Protein, fat and calories were not restricted, participants were counseled to avoid trans fats.

I really like that these researchers applied a fairly strict carbohydrate criteria for their low-carb group. One of the biggest problems with a lot of the low-carbohydrate literature is that the diets being studied are not actually low-carb at all. They might be lower than before, but if you are still eating 200+ grams of carbohydrate a day, that’s not low.

Anyway, after tracking these participants for the full two years, what did they find? First let’s look at some health markers, specifically some blood chemistry results.

HDL cholesterol (so called “good” cholesterol)
Low-carb: +8.4%
Mediterranean: +6.3%
Low-fat: +6.4%

Verdict: All the groups proved beneficial, low-carb provided the strongest benefit.

LDL cholesterol (so called “bad” cholesterol)
Low-carb: -3.0%
Mediterranean: -5.6%
Low-fat: -0.05%

Verdict: Mediterranean proved to be the best, with low-carb also conferring some benefit.

Triglycerides (the actual dangerous blood lipid)
Low-carb: -23.7%
Mediterranean: -21.8%
Low-fat: -2.8%

Verdict: Once again, low-carb was most effectively, with the Mediterranean diet also providing stellar results.

Looking at these results, we see that both the low-carb and the Mediterranean diets were very effective at improving blood chemistry readings, whereas the low-fat diet improved HDL, a good thing, but had little to no effect on either triglycerides or LDL cholesterol.

I’d be remiss if I didn’t point out that the group that ate the highest amount of saturated fat and cholesterol was the low-carb group. Judging from these numbers, they actually experienced the greatest positive change in their cardiovascular health.

Once again, we see the old “avoid saturated fat and cholesterol” mantra does not actually hold up when subjected to scientific scrutiny… or common sense. We evolved off of a diet with ample amounts of both saturated fat and cholesterol, so why it would suddenly start to kill us beginning in the 20th Century is beyond me… but I digress.

Not only were differences found in cardiac risk factors, but significant differences in weight loss were also observed.

N Engl J Med 2008;359:229-41

There’s actually quite a lot going on in this graph, so I’ll just point out three key take home points.

1. For the average Joe or Josephine, both a low-carb or Mediterranean diets are substantially more effective for weight-loss than is a low-fat diet. Does this mean that low-fat diets are useless? Not at all, but if you are currently overweight and looking to drop some pounds, you should adopt a low-carb or Mediterranean diet until proven otherwise.

2. Keeping carbohydrates very low (observe the 2-month, 20 g/day phase in the low-carb group) produces a dramatically more pronounced weight loss than anything else. It’s really not even debatable. Not only are low-carb diets more effective for weight loss, but they are also quite safe, if we accept that improvements in blood chemistry are a desired outcome. In fact, this pattern of rapid weight loss shows up in virtually every single legitimate low-carb study ever conducted.

Of course, while the really low carbohydrate diets are dramatically more effective for weight loss, they aren’t necessarily the easiest to maintain. Although weight does trends back up over time on a low-carb diet, this is less a reflection of low-carb diets losing effectiveness and more a reflection that few people are willing to maintain a strict low-carb lifestyle. That being said, even relaxing your carbohydrate intake up to 120 g/day will still allow you to maintain a significant weight loss for a period of several years.

An Atkins-esque spread

3. The low-carb group also lost the most weight despite not having a calorie ceiling. Remember, the other two groups were expected to limit calories at either 1500 kcal or 1800 kcal.

What this suggests is that if you give an individual sufficient protein and fat, they will self-select a lower amount of calories (obviously not being able to eat carbohydrates helps in this regard) and ultimately control body weight.

Recall, there was really only one diet rule this group followed, 20 g of carbohydrate per day for 2 months, then keep it under 120 g/day. In my opinion, that’s startlingly simple diet advice and as we know, the fewer rules or complicated counting schemes required of a dieter, the greater likelihood of success.

Since I’m on a roll, I’ll toss in a bonus observation…

4. Women tended to lose more weight on the Mediterranean diet than either of the other two. Full disclosure, this wasn’t my observation but one made by the study authors, however it still bears repeating.

The fact that women do better on a higher fat diet (up to 35% of total calories), complete with “lighter” proteins (fish and chicken) is something I have observed quite often working with my own clients. Just a short while ago, I was speaking with Carter Schoffer, one of the founding member of Precision Nutrition and a guy who currently runs and he’s also observed that women tend to lose more weight on a higher fat diet. And this guy is not some internet huckster, but rather someone who has coached thousands of clients through body transformations.

For whatever reason, women seem to more readily settle into a higher vegetable, higher chicken and fish diet than do males. Conversely, males seem to have little problem cutting out grains and most fruits from their diet (which makes Atkins possible), as long as they still get their red meat. However, both groups seem to benefit from swapping carbohydrate energy in favour of either more fat, more protein or both.

Isn’t it telling that the people whose livelihoods depend on looking good, physique athletes, have figured out long ago that strategically reducing their carbohydrates is the best way to get and stay lean? Thankfully, we are now coupling this mass of observational data with an emerging body of literature to support that carbohydrate reduction is the most effective strategy for weight loss and long-term weight control.

But what is even more important, carbohydrate reduction also dramatically improves your cardiovascular risk profile. Which kinda begs the question: if lower carbohydrate diets are more effective for weight loss and are good for your heart, do our supposed health organizations (ahem, I am looking at you American Heart Association) really know what they are talking about?

Just a thought…

Till next time, train hard and eat clean.