Welcome back to my 3-part discussion on the macronutrients. Last week I talked about carbs and this week I’m discussing fat. If you didn’t read last week’s post, I encourage you to do so in order to have a better understanding of how all 3 macronutrients function in the human body.
When I was coming of age, fat was to be feared. This carried through into my early adulthood – my dorm room was FILLED with fat-free food. Even though I knew enough about human physiology, the mere fact that fat is calorie dense was enough of a deterrent for me to avoid dietary fat like the plague.
But, things have changed. Now it seems like fat is being touted for being the answer to weight-loss. You hear about the benefits of the keto diet all of the time.
So why does our take on fat have to be all-or-nothing? It really shouldn’t be! Read on to learn a little bit more about dietary fat and its role in the human body.
It’s about to get science-y. I won’t be offended if you skip ahead!
Let me start by defining a fatty acid, because all fats contain a fatty acid. Ok, so a fatty acid is essentially a chain of carbons, some of which are bond to hydrogen molecules; there is a methyl group on one end and a carboxyl (acid) group on the other end. The length of these fatty acids vary and depend upon the number of carbon atoms in the chain. Still with me? Great. If not, here’s what you need to know: When all of the carbons are bound to a hydrogen, the fat is considered “saturated.” When there are carbons without bound hydrogens, they must form double bonds with their neighboring carbons and therefore the fatty acid is considered “unsaturated.”
Unsaturated fatty acids can be further divided into 2 main categories:
- Monounsaturated fatty acids are missing two hydrogen atoms and therefore have one point of unsaturation.
- Polyunsaturated fatty acids, which are missing four or more hydrogen atoms and therefore have two or more points of unsaturation. The Omega 3 and Omega 6 fatty acids fall into this category.
*Keep this info in mind as we delve further into dietary fats!
Fats or “lipids” fall into 3 main categories:
- Triglycerides – These consist of 3 fatty acids attached to a glycerol backbone. Triglycerides account for 99% of body fat stores and 95% of dietary fat. So, when health professionals refer to “fat,” they are typically referring to triglycerides.
- Phospholipids – These consist of 2 fatty acids attached to a glycerol backbone with a phosphate head. You’ll find these in our cell membranes. Having adequate dietary fat is essential in order to maintain the integrity of our cell membranes.
- Sterols – These lipids have a ring-like structure and are found in both our food and within the human body. The most commonly-known sterol is cholesterol. Cholesterol is only synthesized by animals (including humans). Cholesterol is VITAL for human existence. It forms the basis of bile, sex hormones, adrenal hormones and is needed for our body to synthesize vitamin D. Cholesterol is also necessary to maintain the flexibility and integrity of our cellular membranes.
So let’s talk a bit more about triglycerides. Their main function is simple – they’re an excellent energy source. In fact, fat supplies 60% of our ongoing energy needs throughout the day and there is more fat utilization during exercise. Fats provide 9kcal/gram, compared to 4kcal/gram provided by protein and carbohydrates. Remember, a calorie is a unit of ENERGY! So, fats are twice as energy-dense as carbs and protein. Triglycerides are stored in adipocytes (fat cells) and provide an abundant source of energy. If you read my last post, you may recall that your body can store ~500g of glycogen (a product of carbohydrate breakdown), which equates to 2000 calories. But, there is an unlimited amount of potential fat storage in the human body, which is why we develop fat stores when we eat in a surplus of calories!
Body fat (adipose tissue) has roles above and beyond energy storage. It serves to protect the organs, helps with insulation and plays a hormone role with respect to energy balance regulation. Adipocytes (fat cells) actively secrete hormones called adipokines that help to regulate energy balance. For example, adipocytes will secrete leptin, which is a hormone that serves to decrease appetite. Therefore, the more body fat you have, the more leptin you secrete. Fat can be stored viscerally (around the organs) or subcutaneously (between the skin and the muscle). Visceral fat does pose more health risks than subcutaneous fat. We can further define fat as either brown or white. Brown fat cells contain more mitochondria, and therefore, can actually burn energy to create heat when the body gets cold. On the other hand, white fat cells promote energy storage and tend to be larger. Genetics can influence the amount of brown versus white fat that an individual has, but both forms of fat serve a purpose!
Now that you have a better understanding of the function of fats, let’s look at the types of dietary fats. Recall that saturated fatty acids are straight because of their bonding, and therefore, they tend to be solid at room temperature. Unsaturated fats, on the other hand, have bends in their structure that facilitate a liquid structure at room temperature (this is what makes them “oils”). Of note, most of the fatty acids in coconut oil are short chains of saturated fatty acids, which allows them to liquify at higher temperatures.
So now that you understand the structure of fats a bit more, let’s talk about cooking! You likely have heard about smoke points and many people know to keep the temperature of their cooking oils low enough to prevent this. But, did you know that many fats are susceptible to oxidation? In case you aren’t familiar, oxidation is a process by which reactive oxygen species (aka “free radicals”) are released when bonds are broken. You may be wondering why I explained the structure of fats in such detail, and here’s why – if we consider the inherently unstable nature of unsaturated fatty acids, it’s clear that they are more susceptible to oxidation. Translation: unsaturated fats are more likely to oxidize and release free radicals! Which means that you should NOT be heating oils that contain primarily unsaturated fats (e.g. olive oil and avocado oil)! Keep in mind that when oils are pressed, it creates heat, which is why buying cold-pressed oils is always a better option.
Fats are also susceptible to rancidification, which can occur with exposure to oxygen, heat or light. This is why good quality oils are sold in dark containers! We all know what it smells like when fats have gone rancid, but here’s something to consider – canola oil often contains a deodorizer so that you cannot smell when they go rancid -YUCK!
I’m happy to report that as of June 2018 trans-fats were banned in the US. But, these fats warrant an explanation. Essentially, hydrogen atoms were inserted into polyunsaturated fats to make them more saturated and to improve their shelf life. This process creates a fat that is more solid than liquid (think about margarine – it’s solid because of hydrogenation!). Trans fats have been proven to be deleterious to health, so it’s a good thing that they’re finally banned. But, there is a loop hole that you need to look out for. If there is less than 0.5g of trans fat per serving, it does not need to be included on the label. So instead, be sure to check the ingredients list and skip anything that contains hydrogenated oils.
It’s also worth discussing essential fatty acids – these are our Omega-3 and Omega-6 fatty acids. These fatty acids are considered essential because they must come from our diet. We need them because they are precursors to hormone-like molecules called eicosanoids, which regulate things like inflammation, blood clotting and vasodilation (the ability of our blood vessels to dilate, as with exercise). The Omega-3 essential fatty acids are eicosapentanoic acid (EPA) and docosahexaenoic acid (DHA); they’re generally considered anti-inflammatory. Omega-6 essential fatty acids include arachidonic acid (AA) and dihomo y-linoleic acid (DGLA), and these are considered pro-inflammatory. But, before you swear off all Omega-6 fatty acids, remember that we NEED to have the ability to create an inflammatory response as humans. Inflammation in response to injury is a biological function, so we do need some Omega-6 fatty acids in order to create these responses when appropriate.
But, it does stand to reason that you’d ideally like to consume more Omega-3 fatty acids than Omega-6 fatty acids in order to promote an anti-inflammatory state in your body. From a holistic standpoint, I recommend not exceeding a 2:1 ratio of Omega-6 to Omega-3 fatty acids. That said, let’s look a little bit more into where to find these essential fatty acids in foods. Omega-3 and Omega-6 fatty acids can be consumed directly, or can be derived from a parent fatty acid (linolenic acid and linoleic acid, respectively).
- Omega-3 Fatty Acids:
- Direct EPA: Fish, seafood
- Direct DHA: Fish, seafood, pastured meat, egg yolks from pastured chicken, algae
- Indirect from linolenic acid: flax seed, hemp seed, walnuts, vegetables (including soybeans)
- Omega-6 Fatty Acids:
- Direct DGLA: borage oil, primrose oil, black currant oil
- Direct AA: grain-fed animal foods, liver, egg yolks
- Indirect from the parent acid linoleic acid: corn oil, soybean oil, safflower oil, sunflower oil, cottonseed oil
Now, let’s shift gears and look at what happens when you consume fats. The goal of fat metabolism (aka hydrolysis) is to break triglycerides into fatty acids and glycerol. Cholesterol, on the other hand, is absorbed intact.
Fat digestion starts in the mouth, when fats begin to melt. The salivary glands also release an enzyme called lingual lipase, which starts to break down short and medium chain fatty acids. The levels of lingual lipase decrease throughout our lifetime. But, infants have high levels of lingual lipase, which allows them to digest the fats contained within breastmilk. Fat breakdown continues in the stomach, which mechanically breaks down fat by churning. Additionally, the stomach releases another enzyme called gastric lipase, which provides minimal fat digestion. The small intestine is the primary site of fat digestion. When fats reach the duodenum (the first portion of the small intestine) a hormone called cholecystokinin (“CCK”) is released, which stimulated the gall bladder to release bile and the pancreas to release digestive enzymes. Bile works to “emulsify” fats, which means that it separates the fats into small particles , which improves the ability of the pancreatic enzymes to break them down into glycerol and fatty acids.
Glycerol and fatty acids are absorbed in the small intestine. Shorter chain fatty acids and glycerol are absorbed into the blood and are taken to the liver. Longer chain fatty acid and monoglycerides (one fatty acid still bound to a glycerol) are packaged into a substance called a lipoprotein, which allows the fats to be transported in the watery blood (remember, fats and water don’t mix, so we need to have a way to transport fat in the blood!). You may be familiar with the terms LDL and HDL, and these are both types of lipoproteins. HDL are high-density lipoproteins and are smallest in size. They contain the least amount of triglycerides and the highest amount of protein; they function to grab excess cholesterol and return it to the liver for processing. LDL are low-density lipoproteins. They contain the highest ratio of cholesterol and deliver cholesterol to cells. HDL is typically referred to as “good” cholesterol, while LDL is often referred to as “bad” cholesterol for the reasons listed above. But remember, your body does need some cholesterol, so LDL does serve a purpose and should not be as close to zero as possible! Our blood cholesterol levels are regulated by the liver. The liver produces somewhere between 800-1500 mg of cholesterol per day, which actually contributes to our serum cholesterol levels far more than our diet does. Consumption of dietary fat DOES lead to an increase in both HDL and LDL levels, which is not necessarily a bad thing (keep reading to see why). Cholesterol regulation is complex, but hopefully you now have a better understanding of how cholesterol functions to help transport fat once It’s absorbed.
So what happens when we eat too much fat? A hormone called lipoprotein lipase (LPL) basically re-assembles the fatty acids and glycerol into triglycerides for fat storage. On the other hand, when we have an energy deficit, a hormone called hormone-sensitive lipase (HSL) breaks down adipose triglycerides into fatty acids, which can be used for energy. HSL is inhibited by insulin, which is one reason that poor blood sugar regulation (and insulin resistance) is correlated with obesity. Think about it this way – if your insulin levels are perpetually high because you’re insulin-resistant, you won’t be able to activate HSL and won’t be able to break down fat stores.
So how much fat should you consume? Well, there is no established Dietary Reference Intake (DRI) for macronutrients, but the Acceptable Macronutrient Distribution Range (AMDR) is 20-35% of total caloric intake. So, let’s say for example that your diet is 2000 calories – you’d be eating somewhere between 44-77 grams of fat per day (remember that 1 gram of fat yields 9 calories). Eating too little fat can certainly lead to deficiencies of the fat soluble vitamins (A, D, E, & K), as well as other health problems, as fats are key constituents of our cell membranes.
Excess fat consumption has been linked with cardiovascular disease, high cholesterol and cancer. This topic warrants its own discussion, so I’m going to keep this as brief as possible. These health issues have MUCH more to do with other contributing factors than just high fat intake. For example, smoking, high blood pressure, poorly regulated blood sugar and obesity all are factors that can lead to adverse health outcomes, especially when combined with a high-fat diet. But that makes sense, doesn’t it? Those factors lead to adverse health effects no matter what. Without going into too much detail I will simply mention that the “Diet Heart Hypothesis,” which was formed in the 1950’s and shaped our belief that dietary fat led to cardiovascular disease, was not sound research and has been disproven. So, let’s stop blaming fat intake for all cardiovascular disease and instead look a little more into other lifestyle factors that could be contributing!
No discussion about fat would be complete without at least mentioning the ketogenic diet. Here’s the basic premise – you restrict your carbohydrate intake so that you have little glycogen stores and low blood glucose, then your liver must convert fatty acids into ketones, which are a usable form of energy for all cells in the body. So the idea is that your body will start to use fat stores as an energy source, thereby leading to weight loss. The ketogenic diet is also touted for its ability to regulate blood sugar. But, it was actually developed for people with epilepsy, because the brain preferentially uses ketone bodies an energy source, and body fat provides a steady source of fuel as compared to ever-fluctuating blood glucose levels. Once again, this topic warrants a more thorough discussion, but here’s my takeaway: the keto diet is great for people with neurologic conditions (epilepsy, Alzheimer’s and Parkinson’s), it also has some use for folks who are overweight and not particularly active. But, I do NOT recommend the keto diet if you’re exercising intensely (especially if this includes weight-lifting or doing HIIT-style workouts where you have bouts of anaerobic activity).
So then, where does fat fit into your diet? Here are my takeaway points when it comes to fat consumption:
- We 100% need fat in our diet. Yes, it is calorie-dense, but it also leads to feelings of satiety and fat is absolutely necessary for maintaining the function and integrity of our cells.
- How much fat you ingest depends upon your goals and your activity level, and this truly varies person to person (sometimes day to day).
- Time your fat intake. Fat digestion does take a bit longer than carbohydrate digestion, so I recommend keeping your fat intake low an hour pre- and post-workout. Eat your fats during times where you’re looking for satiety.
- I am far more concerned with the quality of fats versus the quantity of fats consumed.
- I avoid vegetable oils (including soybean oil and canola oil), as they are high in polyunsaturated fatty acids and often contain GMO’s (94% of soy, 90% of canola and 88% of corn grown is the US is genetically modified!). Vegetable oils also go through significant industrial processing that can introduce toxic compounds. Rather, I choose coconut oil and animal fats (including ghee and grass-fed butter) for cooking and use cold-pressed olive oil for dressing.
- I try to aim for a ratio of 2:1 when it comes to Omega-3 and Omega-6 fatty acids. This means, I eat more grass-fed meat and seafood than I do chicken, which is naturally high in Omega-6 fatty acids. I also incorporate hemp and flax seed oil. Keep in mind that flaxseeds are VERY vulnerable to oxidation, so flaxseed oil should be kept in an opaque bottle to protect it from the sun!
- Remember that lifestyle factors play a much larger role in development of cancer and cardiovascular disease. So, be sure to regulate your blood sugar by limiting your refined carbohydrate intake and eating fiber, avoid processed foods, exercise, don’t smoke, drink adequate water and get plenty of sleep! It really is that simple.
Have questions about what your fat intake should look like? Reach out to me – I’d love to work with you!