In Part 1 of this subject we took a look at using google scholar to find research papers.
Let’s take a closer look at the first result returned by the search. This was the search result:
This looks like a relevant study since it does focus on ketogenic diets. Ketogenic diets are typically very low in carbohydrates. Low carb can be a much wider definition and in some cases can be much higher amount of carbohydrates.
Focus of the study?
This study compared Low-Carb and Low-Fat diets. That is a pretty specific focus but it’s even more narrow because the purpose was for treatment of obesity and out-of-bound blood test results.
Type of Study?
There are quite a few types of studies. Not all types of studies provide solid evidence. This particular study is a Randomized Controlled Trial (RCT). Another example of a type of study is a correlation study (see this article for the limits of correlation studies).
Looking at the page
The top of the returned page shows:
The publication is listed as Annals of Internal Medicine. The Date of the page is “18 May 2004” so the study is older. That doesn’t mean it is a good or bad study necessarily but there may be newer studies which add more data to the original. The original search engine result showed that there were over 900 citations of this particular study.
The list of authors for the study includes quite a few people. One of them, Eric Westman is known in the Low Carb community as an advocate of the diet. It is unknown to me if Eric Westman was a supporter of the diet back in 2004.
The other authors seem unfamiliar but searching for research by them might lead to other related papers.
The body of the page
The rest of the page has a summary of the study as well as the actual study data which followed the summary.
Looking at the Summary Section
Background:Low-carbohydrate diets remain popular despite a paucity of scientific evidence on their effectiveness.
In 2004 that may have been true. It’s not true today so it would be dishonest for someone to claim (today) that there’s no scientific evidence of the effectiveness of a low carb diet.
Objective:To compare the effects of a low-carbohydrate, ketogenic diet program with those of a low-fat, low-cholesterol, reduced-calorie diet.
The objective seems on-point but raises questions which need to be answered by looking into the details. It is good that the diet is defined as a ketogenic diet in contrast to other Low Carb diets since that establishes the limit on the carbohydrate levels.
The comparison diet seems to match the standard recommended diet for weight loss which includes:
- Low Fat
- Low Cholesterol
- Reduced Calories
This also raises the question of the amount of fat in the ketogenic diet, the cholesterol level and whether or not the ketogenic diet was reduced calories. There’s quite a few variables being manipulated on the “standard dietary recommendation” diet but many of them may be dependent (not independent variables).
Randomized, controlled trial.
RCTs are typically good science but it bears some examination to see just how randomized the participants were.
Outpatient research clinic.
An outpatient research clinic sees people regularly to check up on progress but people are allowed to go about their day-to-day lives. That’s often a good thing since it doesn’t cause people to live their lives in an unnatural setting.
However, a setting like a metabolic ward allows for other variables to be controlled since food intake is controlled and outputs (urine, etc) are measured and sampled.
120 overweight, hyperlipidemic volunteers from the community.
The number participants was 120 people. That seems like a decent size. They were volunteers so their motivations were unknown. It is not clear whether this particular group is at all representative of typical overweight individuals. They all did have blood test results which indicate that they had bad test results.
Low-carbohydrate diet (initially, <20 g of carbohydrate daily) plus nutritional supplementation, exercise recommendation, and group meetings, or low-fat diet (<30% energy from fat, <300 mg of cholesterol daily, and deficit of 500 to 1000 kcal/d) plus exercise recommendation and group meetings.
So here’s the real details of the diets. The summary seems like it is comparing ketogenic levels of carbohydrates (less than 20g a day). Both grouns got exercise recommendations and group meetings. The first group got nutritional supplements and the second group didn’t.
Again there’s a whole lot of variables here as well as unmentioned items like the protein amounts for each group.
Measurements: Body weight, body composition, fasting serum lipid levels, and tolerability.
The metrics seem useful. They seem designed for the purpose of determining the effectiveness of the diet for lipid levels.
Parsing the Results:
Compliance of the LC group was good since more finished the study as a percentage.
A greater proportion of the low-carbohydrate diet group than the low-fat diet group completed the study (76% vs. 57%; P = 0.02).
Surprisingly Weight loss in the calorie controlled LF group was less than the LC group which didn’t mention any calorie restrictions. This begs the question of how well people in the LF group complied with the study. At between 500-1000 calorie deficit per day they LF group should have lost 1-2 lbs per week. However, the summary lists the percent lost not kg lost. The LC group lost nearly twice the weigh (as a percentage) than the LF group lost.
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).
Fat loss was also greater (and in proportion to weight loss). Unfortunately, the results here were in kg and not in percent so it’s hard to compare the two.
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).
The following numbers were the effects on blood lipids which were favorable to the LC diet and of greater magnitude than the weight loss differences. In fact, the LF diet increased the HDL levels which shows a bad result.
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).
LDL was too close to call but there were some outliers with more in the LC group. This would be higher LDL values in some people which seems common in the LC diet (See our article – Cholesterol and Low Carb Diets) which explains this result in some people (including me) with LC diets.
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.
All in all it looks like LC for the win but if LC came out bad (hasn’t happened yet in any study) we would look at why and report on it.
Studying Research – Part 3 – Study Details