Understand the nutritional impact of dietary fat

Dietary fat is absolutely critical. For example, fat is needed for cell membrane construction, hormone production, and fat-soluble vitamin absorption, and having adequate fat in the diet can have a favorable impact on satiety, to an extent. We often categorize dietary fats based on the structure of their hydrocarbon chains, which requires us to think back to our most recent biochemistry class. If all of the chemical bonds along this hydrocarbon chain are single bonds, it’s a saturated fatty acid. If the chain contains one double bond, it’s a monounsaturated fatty acid. If the chain contains two or more double bonds, it’s a polyunsaturated fatty acid.

Structure of (a) saturated and (b) unsaturated fatty acids

Most of the time, the double bonds in unsaturated fatty acids have a “cis” configuration, in which the functional groups are on the same side of the hydrocarbon chain. However, if a fatty acid contains one or more double bonds with the “trans” configuration, the functional groups will be on opposite sides of the chain, and the fatty acid is categorized as a trans fatty acid. You’ve probably heard of these categories before; it’s very common for food labels to list not only the total fat content of the food, but also the amount of saturated fat and trans fat.

When unsaturated fatty acids undergo hydrogenation, the configuration of certain bonds changes from the cis orientation to the trans orientation, as shown above

Fat had a pretty bad reputation from the 1950s up through about the 1990s, which was largely overblown. However, dietary fat has made a huge resurgence, largely fueled by increasing popularity of the ketogenic, carnivore, and paleo diets, and the resulting glorification of dietary fat is also a bit overhyped. When people set their sights on making evidence-based decisions about dietary fat sources, they often focus on the cholesterol, trans fat, and saturated fat content of the food. It’s counterintuitive, but dietary cholesterol intake probably doesn’t have a huge impact on blood cholesterol levels; the US guidelines used to recommend keeping dietary cholesterol below 300mg/day, but they have removed this guideline in recent years.

Most dietary trans fats are synthetically produced by a process called hydrogenation, which converts double bonds to single bonds and gives the food item more favorable properties for cooking, texture, and shelf stability. We generally see dietary trans fats in the form of partially hydrogenated oils; there seems to be a pretty universal consensus that these artificial trans fats are pretty bad for cardiometabolic health outcomes, so most dietary guidelines recommend avoiding them as much as possible. There are also small amounts of naturally occurring trans fats found in the meat and dairy products from ruminants. While evidence clearly demonstrates that artificial trans fats are bad news, the data related to naturally occurring trans fats are pretty inconclusive; it’s not clear if this is because there’s a true difference in risk, or because the naturally occurring trans fats appear in pretty limited amounts, thus capping intake at a low enough level to avoid deleterious effects.

While trans fatty acids are far more deleterious than saturated fatty acids, it might not be a bad idea to at least keep an eye on saturated fat intake. There’s a lot of misinformation out there about fats; some people demonize saturated fats to an unjustifiable degree, while others treat polyunsaturated fats as if they’re poison. There’s no reason to aggressively avoid either, but it’s worth noting that high saturated fat intakes are associated with some unfavorable effects on blood lipids, and replacing saturated fat with unsaturated fat has been linked to reduced mortality risk.

Beyond their degree of saturation, fatty acids can also be categorized based on whether or not they’re essential. Much like essential amino acids, essential fatty acids cannot be created by our bodies in sufficient amounts, so we have to get them from our diet. Once again, this categorization comes down to the chemical structure of the hydrocarbon chain. All essential fatty acids are polyunsaturated, but not all polyunsaturated fatty acids are essential; the location of the final double bond is what ultimately dictates whether or not a fatty acid is essential. The very end of the hydrocarbon chain is labeled as the “omega” end, and we count the chemical bonds backward from that point.

If we count back from the omega (ω) end, we can see where the final double bond is located for omega-3 (ω-3) and omega-6 (ω-6) fatty acids

Humans have the ability to synthesize some unsaturated fatty acids, but we don’t have the enzymes required to insert double bonds at the omega-3 (3rd bond from the end of the chain) or omega-6 (6th bond from the end of the chain) position. As a result, there are two fatty acids that are truly essential for humans: alpha-linolenic acid (an omega-3 fatty acid) and linoleic acid (an omega-6 fatty acid). If we have adequate intake of these fatty acids, we can synthesize all sorts of derivative omega-3 fatty acids (such as eicosapentaenoic acid [EPA] and docosahexaenoic acid [DHA]) and omega-6 fatty acids (such as gamma-linolenic acid, dihomo-gamma-linolenic acid, and arachidonic acid).

You’ve probably heard of EPA and DHA before, because they’re the two most notable fatty acids in fish oil. While it’s true that we can create EPA and DHA if our diet has plenty of alpha-linolenic acid in it, these conversions are very inefficient, and there are many plausible benefits associated with increasing the EPA or DHA content of various tissues throughout the body. For example, the fatty acids in fish oil have been linked to positive impacts on a wide variety of things including cognition, mental health, inflammation, immunity, muscle protein balance, and neuromuscular function, all with varying degrees of evidence.

As a result, it’s very common for people to supplement with marine sources of EPA and DHA, most commonly from algae oil or fish oil supplements, in order to get these fatty acids directly from the diet instead of relying on inefficient conversions from alpha-linolenic acid. Omega-6 fatty acids are typically easier to come by in the diet, so supplementation with omega-6 fatty acids is far less common. Whether you choose to supplement or not, you definitely want to make sure you’re getting sufficient essential fatty acids from your diet, which may require extra attention if you’re on a pretty low-calorie diet with limited fat intake. If you use MacroFactor, your intakes of EPA, DHA, total omega-3, and total omega-6 fatty acids are all easy to monitor.

Incorporating Fat Into a Diet

Dietary fat is important for health, so insufficient intake is bad news. We want fat in our diet so we can build cell membranes, absorb fat-soluble vitamins, obtain essential fatty acids, and keep our sex hormones within typical ranges. However, if fat intake gets too high, it could start to displace protein and carbohydrate, which also isn’t ideal for the typical lifter with goals related to high-intensity performance or body composition. Generally speaking, dietary fat often constitutes between 20-35% of a lifter’s total energy intake if they’re consuming a fairly moderate level of total energy (that is, not super low caloric intake, and not super high caloric intake). Even if you’re not a lifter or avid exerciser, this range also works out pretty well for sedentary folks, although their need to preserve carbohydrate in the diet isn’t quite as pressing.

In conjunction with this range of 20-35% of energy, it’s a good idea to establish a lower limit for fat intake, just to make sure that this percentage-based range doesn’t lead to insufficient fat intake when calories are low. A lot of people set the lower threshold based on kilograms of total body mass, and typically set it around 0.5-0.6 grams of fat per kilogram of body mass. So, if you weighed 100kg, you’d never let your dietary fat intake get below 50-60 grams per day.

This approach works pretty well for a decently large percentage of the population, but we aren't totally convinced that it’s a truly optimal solution. Dietary fat requirements shouldn’t be expected to scale dramatically upward with increasing adiposity or increasing fat-free mass. In addition, people with higher body weights might be more inclined to adopt fairly low-calorie diets in order to lose a substantial amount of weight in a timely manner. It would seem counterintuitive to insist that someone in that scenario needs to eat more daily fat than a leaner person with similar goals. On the contrary, extremely lean individuals probably have to be more cautious about insufficient dietary fat intake than people with more stored fat mass. In summary, setting a lower limit for fat intake based on total body mass or fat-free mass might lead to unnecessarily high fat intake for dieters with higher body weights, and could also enable inadvisably low fat intakes for some dieters with lower body weights.

Based on these shortcomings of weight-based lower thresholds for fat intake, it probably makes more sense to set the lower fat threshold based on height rather than body mass. Individualized recommendations for fat intake can be challenging to make; most governments and nutrition organizations make fat intake recommendations based on a percentage of calories consumed, while assuming that calorie needs generally increase with increasing stature. It also seems plausible to assume that individuals of larger stature may require slightly more fat intake to support essential fatty acid incorporation into various types of cells and tissues that larger people have more of. By scaling the lower threshold for fat intake based on height, minimum fat requirements can scale upward for people of larger stature, while avoiding paradoxical situations where people who need fat the most (super lean people on low-calorie diets) have very low recommendations for fat intake, or people who need fat the least (people with a large amount of body-fat who wish to lose weight) have relatively high recommendations for fat intake.

If you’re below 150cm, then you probably don’t want to go below 30g/day of dietary fat intake. If you’re 150cm or above, then a reasonable lower threshold can be calculated by subtracting 150 from your height (in centimeters), then multiplying the outcome by 0.5, then adding 30.

As a reminder, this is for setting the absolute lower limit, not your target intake. For establishing a target intake, a good (but generalized) estimate would be to aim for somewhere between 20-35% of total energy from fat if your total caloric intake is pretty moderate, or 0.7-1.5g/kg of body mass if your calorie intake is pretty high or pretty low. Whether you err toward the lower or upper end of this range would be dictated by how carbohydrate-dependent your exercise of choice is, and how much you prefer carbohydrates to fats (or vice versa). Obviously, if you calculate a target fat intake value (based on percentage of total energy or grams per kilogram of body mass) that ends up below your previously calculated lower limit, you would raise your daily fat intake target to a value that is equal or greater than the lower limit. MacroFactor uses a height-based lower fat threshold in combination with percentage-based fat targets that align with your stated goals and preferences in order to provide optimized recommendations for daily fat intake, while never going below the advisable lower limit value.

Finally, when it comes to specific types of fat, a simple but effective strategy is to limit artificial trans fats as much as possible, and to get a roughly even split of dietary fat from monounsaturated, polyunsaturated, and saturated fats. Keeping a decent amount of polyunsaturated fat makes it easier to consume plenty of EPA, DHA, and essential fatty acids. Numerous health organizations across the globe recommend around 0.3-0.5g/day of combined EPA and DHA intake for general health, but most people who supplement with fish oil or algae oil supplements tend to aim for around 1-3g/day in hopes of obtaining additional health, performance, or body composition benefits. Whether or not supplementation leads to additional benefits is often debated and varies from outcome to outcome, but that particular discussion is beyond the scope of this knowledge base entry.

There are several different types of dietary fats, which all have a place in a balanced diet

Keeping a decent amount of monounsaturated and saturated fat in the diet appears to support sex hormone production pretty effectively. Most guidelines related to cardiovascular health advise keeping saturated fat to no more than 10% of total energy intake, so if you follow the recommendation of getting 20-35% of calories from total fat with an even mixture of monounsaturated, polyunsaturated, and saturated fat, you’ll be under or close to that limit. Of course, if well over 30% of your energy intake is coming from fat, you might potentially consider keeping your saturated fat a little lower than your monounsaturated and polyunsaturated fat intakes. Just as the purported benefits of high fish oil intake are controversial and aggressively debated, there is much debate surrounding the relationship between saturated fat and cardiometabolic health. That’s another nuanced debate that exceeds the scope of this knowledge base entry, but interested readers should check out a great 3-part article series by Alan Flanagan of Sigma Nutrition (one, two, three).

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