The skinny on saturated fat and where it sits in the context of a calorie deficit

Even in 2021, there is still a repeated back and forth argument among enthusiasts and even some health professionals about saturated fat when you start discussing the dietary good and bad's about it.

I'd like to piece together some scientific evidence and a sprinkle of clinical rationale to look more closely at how saturated fat behaves in the presence of an energy deficit.

Authors note as of finishing this piece: I originally wanted to dive into the saturated fatty acid sub-types within different foods and see what influences they have on cardiovascular health but this article turns out to be quite long and it would only add more details to an already lengthy article so I'm better off doing this in a separate piece.

The key question is: What happens when we lower the required calories that the body demands to produce a hypo-caloric state and yet still feed it with a large amount of dietary saturated fat?

When trying to answer this question, let's consider that this isn't as commonplace to find as I would have thought, especially when it comes to saturated fat sub-types (i.e. those in different dairy fats or other animal fats). Most of the evidence looking into effective diet types doesn't really look to label the energy deficit based on saturated fat compared with unsaturated fat. This means we have to look at the diet types used in studies and see how much saturated fat makes up a percentage of those diets as well as the absolute amounts of saturated fat (in grams) within each diet compared with other diets and see what the result is on CVD health.

So I'm being transparent from the start, my hypothesis - as the proverbial fence-sitter in most nutritional considerations that I am - is something akin to this: I would rationalise that the higher amounts of saturated fat in the diet compared to what many organisations like the World Health Organisation (WHO) and American Heart Association (AHA) recommend becomes much more insignificant in the context of an energy deficit, particularly so as it pertains to what happens with the associated weight loss markers tied to this (in particular, blood lipids).

There are plenty of examples around of studies which compare a calorie deficit with different macronutrient compositions (eg. low carbohydrate diets compared with low fat diets; or 'lower' carbohydrate diets compared with ketogenic diets). As a bonus, most trials now generally control for protein given its the most essential macronutrient that the body demands in large amounts on a daily basis.[1]

The key question is: What happens when we lower the required calories that the body demands to produce a hypo-caloric state and yet still feed it with a large amount of dietary saturated fat?

So on this and before we dive into a few of the studies as something of a very small research review of what's out there, keep in mind we might need to work indirectly on diets which contain more total fat, or are more ketogenic in their nature because it indicates they will likely have a higher absolute amount of saturated fat in them.

I will randomly report on three studies I find through searching Google Scholar and PubMed to review. In other words, I will use some basic key terms like 'saturated fat' and 'weight loss' (and their synonyms) to see what comes up and just select articles that are titled clearly. Of course this could be done much more systematically, but it is a blog post after all and systems take more time and more thought, but especially time.

Does someone losing weight - that is body fat, not just any kind of weight - still eating a higher saturated fat diet override the more detrimental effects of saturated fat?

What does saturated fat do?

While I did mention this article is not about saturated fat directly being good or bad, it is still important to look at what the roles and functions of it are as well as why this question might be important for multiple reasons:

• It provides a source of energy (as does all fat) at 9 kcal (37 kj) per gram.
• It can act as a carrier of fat soluble vitamins A, D, E and K and other fat soluble substances.
• The internal cell architecture can be stiffened by saturated fat intake which may decrease cell fluidity and function of some of its internal moving parts.
• Also, saturated fats constantly get reported as playing a role in the synthesis of hormones like testosterone. However, this should be made clear that it's usually because saturated fat raises dietary cholesterol levels and it's the cholesterol that increases the production of some different classes of hormones (including testosterone and oestrogen).[2]

So we can see that some functions are what we'd call beneficial and others not so beneficial. Why the question I'm trying to answer becomes more important is really due to the effect of weight loss that's thrown into the mix.

Does someone losing weight - that is body fat, not just any kind of weight - still eating a higher saturated fat diet override the more detrimental effects of saturated fat listed above?

Chewing the fat - the types of fat and in what amounts?

Study 1: Klempel et al.

Let's start with a basic comparison of a high fat diet compared with low fat diet by Klempel and colleagues.[3] This study also used the alternate day fasting method which should be mentioned, despite that it's much of a muchness comparing fasting-type diets with standard calorie restriction diets.[4]

So in the two diets run over 8 weeks, the higher fat diet contained 100 grams of fat per day and 30 grams came from saturated fat. The lower fat diet contained 55 grams of fat and 13 grams from saturated fat. Also just for reference, the American Heart Association recommend that people consume no more than 13 grams of saturated fat per day in a standard intake of 2,000 kcal/day. So in this instance, even the lower fat diet in the study contained as much as what the AHA recommends not going above.

So besides both groups losing around 4-5 kg of weight, what happened to other markers of health measured? Both groups decreased their levels of LDL cholesterol (the 'bad' one) and triglycerides (another 'bad' marker in excess in the blood). HDL cholesterol (the 'good' one) either stayed the same or increased slightly.

See the table above for details. They were reported as statistically non-significant between groups and the margins were very small between diets. Nonetheless, all markers were generally favourable due to the fat loss.

Study 2: Sacks et al.

The second study was performed by Sacks et al. and it looked at four different diets that also manipulated protein intake over two years. [5]

Of note: Anything longer than 12 months is typically considered 'long-term' by definitions but this term is somewhat malleable. Some researchers will say three months can be 'long-term' under some situations while others won't consider it as such until it's five years in length. The big difference in definitions is the point, but from a dietary perspective, two years always looks good to gather real-world events.

So Sacks and his team looked at 811 overweight and obese adults and checked in with their adherence to these diets at three time points to take blood and other measures (the first follow-up was at six months and the second follow-up was at two years).

When we break down the content of fat in the diet what do we know? Well first, both higher fat diets contained 40% as total fat (this was slightly less as a percentage of total dietary fat compared with Study 1 by Klempel). However, protein wasn't constant and as we said earlier this can change things because higher protein leads to greater weight loss results and can skew the results with fat in the diet.[6]

Another caveat in this paper was that authors stated that one of the other dietary goals "...for all groups were that the diets should include 8% or less of saturated fat...". However, both high fat groups did not do this in practice. They both ate slightly above the limit that was told to them by the researchers (which was about 10% total saturated fat in each time point). What does this mean? It makes the overarching question harder to answer because 10% of saturated fat in the diet is still just on the WHO recommendation at 10%. We can still look at the researcher's table (image below) to see some differences in terms of what was statistically significant compared with what wasn't. Absolute amounts of SFA (in grams) were not reported in this table.

In brief and with markers of importance with dietary saturated fat, we can suggest that triglyceride levels dropped similarly between all four diet groups even in the higher fat groups, where participants ate more saturated fat than they were advised too (12-17% as a range).

Also, the LDL ('bad') cholesterol was significantly decreased more in the lower fat groups than the higher fat groups of the study (5% cf. 1%). All diet types lowered from baseline however. On the other hand, HDL ('good') cholesterol was significantly increased in the higher fat groups compared with the lower fat groups (9% cf. 6%). And again, all diets increased from baseline.

What does all this jargon basically say? Weight loss is good for biomarkers irrespective of how much (or how little) fat was in the four diet types. Yes, they ate slightly more saturated fat than they were told too, but it didn't seem to make too much difference - which is good. Another tick for weight loss as the primary mediator of improving health.

Study 3: Shih et al.

The last study we'll take a look at was a secondary analysis of a larger trial called the Diet Intervention Examining The Factors Interacting with Treatment Success (DIETFITS).[7] In this study, the authors took 208 people (from the original study of 609) who were assigned to the healthy low carbohydrate group and then analysed and adjusted for their percentage of saturated fat (%SFA) in the diets they consumed over 12 months.

They then contrasted the amount of saturated fat consumed with their lipid blood markers - in particular blood triglycerides, LDL and HDL cholesterol - over the 12 months. What they found was that while the study focus was on dieting, the energy deficit (per day) for each participant was ~500 kcal but the increasing percentages (expressed as tertiles in this paper) of saturated fat within this diet went up in ranges between 12-18% (higher than recommendations cited earlier by the WHO).

There's at least two interesting points about what happened to blood lipid markers measured after the twelve months. One point I want to discuss occurred in the healthy low carbohydrate group, which is directly relevant to our question, the other occurred in the healthy low fat diet group compared with the healthy low carbohydrate group.

1) Within the healthy low carbohydrate diet group, by the end of the 12 months there was as much as 20 grams per day of change in dietary saturated fat with the lowest tertile compared with the highest tertile - which is quite substantial (see the table below). It makes it harder to break down this situation because the highest tertile were the only ones in the healthy low carbohydrate group who were still eating more saturated fat compared to when they were at baseline (i.e. the amount of saturated fat they were eating when starting the study compared with when finishing it).

So using pure amounts (grams not percentages) means we're probably best to isolate this group for the sake of the study and it's most reflective of real world accuracy too. So what's the main thought experiment in all this? Well, the highest tertile consumed 9 grams more saturated fat than when they started the diet (the average was 30 grams at baseline) after 12 months but they were eating healthier foods and running an energy deficit. This means that the highest tertile were eating nearly 40 grams of saturated fat per day - three times higher than the AHA recommendation of 13 grams/day or less in absolute terms.

All tertiles lost significant amounts of weight (~ 6.3 kg) over the year as the primary marker but what happened to their blood lipids? Triglycerides decreased, HDL cholesterol increased (both non-significantly) and LDL cholesterol also increased (non-significantly) within the groups. In other words we could say based on these figures that a healthy low carbohydrate diet with a relatively high percentage of saturated fat in it favours a slightly beneficial effect on triglyceride and HDL cholesterol and a slightly detrimental effect on LDL cholesterol but all were not statistically significant when adjusted for age, gender, race, weight changes and 12 month carbohydrate intake.

2) When we look at the second important aspect - the inclusion of the healthy low fat diet group from the original study - significant differences were observed. The healthy low fat diets had significantly lower LDL than the healthy low carbohydrate diets, while the lower carbohydrate group had significantly higher HDL cholesterol and significantly lower triglycerides.

Simply speaking (and as expected), all the diets worked by way of weight loss, but the healthy low carbohydrate diet had more favourable effects than the healthy low fat diet on HDL cholesterol and on triglycerides even though saturated fat percentages all increased from baseline.

To conclude: What happened with our blood lipids eating saturated fat when the calorie deficit was there?

Arguably - and using only these three studies and a combined sample of 1051 people - we can say with some reasonable confidence that the loss of body weight and in particular body fat appears to have either beneficial or neutral effects on the blood biomarkers typically used when discussing higher saturated fat within the diet. These markers as discussed were triglycerides, LDL cholesterol and HDL cholesterol. However, more advanced lipid testing was not a part of any of these studies and may shed more light on the behaviour of dietary saturated fat (and our genes), so bear this in mind. Nonetheless, we still have to take the data as it were in the above studies.

A caveat in all of this is probably that the total amount of saturated fat just wasn't high enough to do anything harmful because all studies are weight loss studies and so the absolute amounts of saturated fats within the diets here may not be enough to cause significant issues. In the contrary, two of the three studies had saturated fat in the 30-40 gram range, which is much higher than the absolute recommendations by the American Heart Association's figure of 13 grams and the WHO's rule of no more than 10% of total calories.

All this could be said to imply - with some clinical caution - that people who have a goal to lose some weight don't have to be as concerned with saturated fat's negative effects typically stated by some organisations and this is because they generally presume (rightly so in many cases) that people are eating either at energy balance or in an energy surplus and the latter causes body fat gain and can be problematic in many instances when done chronically over time.

I think the hypothesis I mentioned earlier seems to hold up okay, however the limitations are plentiful and I only looked into three papers randomly. If there is anything else out there, please feel free to message me or let me know in the comments if you see anything worth looking at more closely. This will help us get our heads around this interesting aspect of nutritional and dietetic science.

References

[1] Simpson SJ, Batley R, Raubenheimer D. Geometric analysis of macronutrient intake in humans: the power of protein? Appetite. 2003 Oct 1;41(2):123-40.

[2] Berg JM, Tymoczko JL, Stryer L. Biochemistry. 5th edition. New York: W H Freeman; 2002. Section 26.4, Important Derivatives of Cholesterol Include Bile Salts and Steroid Hormones.?Available from: https://www.ncbi.nlm.nih.gov/books/NBK22339/

[3] Klempel MC, Kroeger CM, Varady KA. Alternate day fasting (ADF) with a high-fat diet produces similar weight loss and cardio-protection as ADF with a low-fat diet. Metabolism. 2013 Jan 1;62(1):137-43.

[4] Trepanowski JF, Kroeger CM, Barnosky A, Klempel MC, Bhutani S, Hoddy KK, Gabel K, Freels S, Rigdon J, Rood J, Ravussin E, Varady KA. Effect of Alternate-Day Fasting on Weight Loss, Weight Maintenance, and Cardioprotection Among Metabolically Healthy Obese Adults: A Randomized Clinical Trial. JAMA Intern Med. 2017 Jul 1;177(7):930-938. doi: 10.1001/jamainternmed.2017.0936. PMID: 28459931; PMCID: PMC5680777.

[5] Sacks FM, Bray GA, Carey VJ, Smith SR, Ryan DH, Anton SD, McManus K, Champagne CM, Bishop LM, Laranjo N, Leboff MS. Comparison of weight-loss diets with different compositions of fat, protein, and carbohydrates. New England Journal of Medicine. 2009 Feb 26;360(9):859-73.

[6] Lauran M, Hosseini M, Ali KM. The effects of hypocaloric, high-protein diets on cardiovascular risk factors and weight loss in metabolically healthy obese adults: a systematic review. Authorea Preprints. 2021 Jul 22.

[7] Shih CW, Hauser ME, Aronica L, Rigdon J, Gardner CD. 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. Am J Clin Nutr. 2019 Feb 1;109(2):433-441. doi: 10.1093/ajcn/nqy305. Erratum in: Am J Clin Nutr. 2020 Feb 1;111(2):490. PMID: 30649213; PMCID: PMC6367958.

I would also like to give credit to the authors of the three papers above for using their data tables to illustrate examples given throughout this article.