“Lipid profiles improved with saturated fat on a low-carbohydrate diet” (View on Flickr.com)
I re-discovered this study while reviewing the studies other that were sent to me purporting to show harm from eating meat or dairy fat (they didn’t). I needed a breath of fresh air from the compromises/conflicts I felt when reviewing the previous two studies done at Harvard School of Public Health.
This one comes from Stanford, and as I’ll point out, has key differences that are immediately and pleasantly obvious, especially in comparison to the previous articles (see: Just Read: Dairy fat, not associated with cardiovascular disease – How to make it look like it is and Just Read: Saturated Fat in Meat is not associated with Cardiovascular Disease – How to make it look like it is).
I actually reviewed this one when it came out (Just Read: DIETFITS new analysis showing benefits for low carbohydrate over low fat diets for blood lipids – changing the focus from weight to metabolic health), however, I’m using the same method I used in the previous posts to evaluate this one, with an analogous graphic, as an example of work well done.
Like the previous studies I reviewed, this one asks, also, about the health impact of saturated fat in the diet. It uses a more proximal/narrower outcome of lipid profile, compared to cardiovascular disease incidence. The study is not asking a much larger question of “what should I eat” which I can now see was a major issue of previous two studies reviewed.
This question is much more fit for purpose in the context of the study that it’s in the context of – which is a randomized controlled intervention trial of eating a whole food based low carbohydrate diet vs a whole food based low fat diet.
- Is there conflict of interest on the part of the authors / study?
- This includes financial as well as intellectual
- Is the methodology fit for purpose for the question being asked?
- What are the results, and are they robust?
- Is there newer/better research out there on this topic?
- I read the whole paper
- I grab the supplemental materials – often the real conclusions are stuffed there
- I look up any tools used, including food frequency questionnaires
Conflict of Interest
Financial conflict of interest – none
None of the authors reports a conflict of interest related to research presented in this article.Shih, Cynthia W, Michelle E Hauser, Lucia Aronica, Joseph Rigdon, and Christopher D Gardner. “Changes in Blood Lipid Concentrations Associated with Changes in Intake of Dietary Saturated Fat in the Context of a Healthy Low-Carbohydrate Weight-Loss Diet: A Secondary Analysis of the Diet Intervention Examining The Factors Interacting with Treatment Success (DIETFITS) Trial.” The American Journal of Clinical Nutrition 109, no. 2 (February 1, 2019): 433–41. https://doi.org/10.1093/ajcn/nqy305.
In contrast to the institution previously discussed (Harvard School of Public Health), there is no investigative journalism concerning undisclosed financial ties that I’m aware of.
Intellectual conflict of interest – present, with balance
Once we get past looking at financial conflicts, intellectual conflicts can factor in. The quote below illustrates the importance. Here’s the quote in full, by Salim Ysuf, Professor, McMaster University:
“Most people don’t read the whole paper, they read the abstract. (When I was at the NIH) …anything that came in that contradicted (low fat) was poo-poo’d. I believe the biggest conflict of interest is your inherent belief system”Food for Thought: the science and politics of nutrition – Day 2 – June 15, 2018’ – youtu.be/Yyhx3C1paA0?t=23130
The situation of this study team seems to be a good example of the pervasiveness of bias (we all have them) and not that they should be eliminated, however, they can be mitigated, as so much research has shown in other fields.
- Chris Gardner, PhD (@GardnerPhD) (principle investigator) could be described by the term “plant-biased” – his writings and social media postings clearly state/imply a bias against animal source eating patterns. This overview of a course he’s teaching at Stanford has the classic “where did the meat go” imagery. Having worked in a large health organization as large (or much larger) as Stanford, I know that images selected for media like this are done with great intention and send a specific message. In this case, it is that plant-based eating is felt to be preferred as a lifestyle.
This bias can manifest in articles like this because there is a known hostility to low-carbohydrate eating patterns among people who are vegans or vegetarians. Even though “low-carbohydrate” does not imply food source, only macronutrient, it is considered by many to be an animal-source dominant eating patten. I could go into this more, but I’ll leave it there, unless there are questions.
- Lucia Aronica (@LuciaAronica), a co-author, I would consider to be biased in a parallel/opposite direction. She’s an advocate of a low-carbohydrate eating pattern and appears in several venues promoting this lifestyle.
I don’t have awareness of any of the additional authors’ potential intellectual biases.
The biases present could lend alternatively to downplaying any benefit of saturated fat (which is often assumed, incorrectly, to be the domain of animal sourced foods only), or promoting it. These are items helpful for the reader to know as they interpret the writing. As discussed in previous blog posts, differences can be sometimes be seen in how data is presented.
Methodology – Random 24-hour dietary recall, not an annual food frequency questionnaire
This is a secondary analysis of a well-designed randomized control trial (The DIETFITS study), so it has the disadvantage of being an observational study, the advantage of connection to an actual intervention.
As with the other studies, I reviewed the dietary recall approach & this seems much more robust. Researchers used an unannounced software-based 24 hour dietary recall “within a 2 week window.” The tool is not available for review, however, a description of the software as well as the output is available:
- Home – NCC: Nutrition Coordinating Center – Nutrition Data System for Research
The output from this software looks orders of magnitude more detailed than what comes from an annual food frequency questionnaire. Recall bias could still be a problem, and one day doesn’t represent a year of eating (and vice versa). Given that the question is really narrow and is not intended to guide health decisions, this methodology is far more fit for purpose than the Harvard examples are.
The DIETFITS study as a whole is a randomized-controlled trial, with its critiques, and in my view is extremely well done compared to what exists in the nutrition space. The article (reference at bottom) links to a paper covering the methods in detail.
As shown in the chart above, a statistically adjusted model shows that lipid profiles overall improved for people who increased their saturated fat while on a low-carbohydrate diet. Those who ate a high-carbohydrate (low fat) diet did not fare as well, with degradation in their lipid profile.
For non-clinicians (or even some physicians) – it’s now known that fasting triglycerides are a much more important marker of cardiovascular health than previously thought, so a reduction here is quite significant. LDL has importance, however/and newer tests such as particle count and size may weigh on this importance. Those tests were not reported in this article. For a good overview of triglycerides, see the AHA scientific statement (Just Read: Triglycerides and Cardiovascular Disease – American Heart Association Scientific Statement).
On balance, then, a stable LDL, HDL, and lower triglycerides is definitely “improvement” for the low-carbohydrate group. An increased LDL, stable HDL and triglycerides is definitely a “degradation” for the high-carbohydrate group.
These findings are consistent with other research on the topic. Maybe the high carbohydrate eating result is not expected, given this pattern conventionally thought of as a method to reduce LDL cholesterol, especially when paired with plant oils. As concluded here, it is shown that the combination of dropping carbohydrate % is part of the significant improvement – it is not associated with saturated fat by itself.
- Several things noticed by the researchers and myself:
- The saturated fat intake in the high saturated fat intake group isn’t that high compared to other studies I’ve seen (see: The Sad Saga of Saturated Fat)
- The increase in saturated fat % is higher in groups that started with a lower saturated fat % and lower in people who started with a higher saturated fat %.
What this means is that the effect on lipid changes could have been greater (or lesser) in a different type of low-carb study.
Some of this can be explained by the way the DIETFITS study was conducted, and in this clip you can see Gardner discussing the direction for subjects to eat lots of vegetables. This is definitely one way to do a healthy low-carbohydrate diet. A different research approach might not emphasize plants as much and could have arrived at a higher saturated fat intake at the end. This is where different views about diet come into play.
I noted in my original review of the DIETFITS study that the high-carbohydrate group significantly moved their lipids to an insulin resistance pattern compared to the low-carbohydrate group, and this difference, which favors low-carbohydrate, was barely mentioned or highlighted in the original article.
For this article, the results, methodology, and recommendations (or lack thereof) align well.
Is there newer/better research available?
The findings in this article are concordant with the body of knowledge already available regarding saturated fat intake and diet. It’s well described that people who ingest saturated fat may have a tendency toward higher LDL (although not the case here), higher HDL, lower triglycerides, and lower serum saturated fatty acids (again, see The Sad Saga of Saturated Fat) . In addition, the finding that absolute amount of saturated fat doesn’t increase, although % calories of saturated fat may increase on a low-carbohydrate diet is also well described. In this sense, it’s important that DIETFITS did not show a lipid profile disadvantage to increased saturated fat in a low-carbohydrate diet.
The for-profit, low-carbohydrate diet company Virta Health has published an analysis of their study showing similar benefits from the low-carbohydrate diet. I would also refer people to the PURE study (observational, food frequency questionnaire) as well as the other studies I mentioned previously.
- JACC State of the Art Review on Saturated Fat – See: Saturated fat does not clog the arteries, increase CVD risk or increase diabetes risk. The end.
- NUTRIrecs series – See: Most important part of this week’s published nutritional guideline recommendations – personal preferences and values are respected
- The PURE study – See: Just Read: More Validation of Low(er) Carb High(er) Fat Diets: The PURE Study and Lipids
- Bhanpuri, Nasir H, Sarah J Hallberg, Paul T Williams, Amy L. McKenzie, Kevin D Ballard, Wayne W Campbell, James P. McCarter, Stephen D Phinney, and Jeff S Volek. “Cardiovascular Disease Risk Factor Responses to a Type 2 Diabetes Care Model Including Nutritional Ketosis Induced by Sustained Carbohydrate Restriction at 1 Year: An Open Label, Non-Randomized, Controlled Study.” Cardiovascular Diabetology 17, no. 1 (December 1, 2018): 56. https://doi.org/10.1186/s12933-018-0698-8. (Virta Health, for-profit company promoting low-carbohydrate nutrition)
Conclusion – Results and Methodology support the answer
For the reasons that the research question is appropriate, the data collection is as robust as the conclusion made, and this paper aligns with other research on the topic, its an example that can be used to support understanding of the impacts of saturated fat in the diet.
Shih, Cynthia W, Michelle E Hauser, Lucia Aronica, Joseph Rigdon, and Christopher D Gardner. “Changes in Blood Lipid Concentrations Associated with Changes in Intake of Dietary Saturated Fat in the Context of a Healthy Low-Carbohydrate Weight-Loss Diet: A Secondary Analysis of the Diet Intervention Examining The Factors Interacting with Treatment Success (DIETFITS) Trial.” The American Journal of Clinical Nutrition 109, no. 2 (February 1, 2019): 433–41. https://doi.org/10.1093/ajcn/nqy305.