Nitty Gritty on Fat Intake Part 1
Fat is a divisive topic. In fact I believe it’s so divisive and prone to wild claims because of how complex our fat physiology is. For a long time, we didn’t have robust research evidence that fat did much more than hold extra calories. More recently, science has discovered that fat (and unless I say dietary fat, I am referring to body fat) is quite hormonally and metabolically active, impacting a wide range of physiology.
Fat has a very large impact on hunger and satiety, fat produces leptin, with leptin signaling hunger/satiety to the hypothalamus, regulating our energy intake. Leptin has impacts on insulin sensitivity, initiation of puberty, initiation of menses, immune system functioning, liver metabolism and a host of other processes.
Fat also has a series of immune system responses that regulate insulin sensitivity. Essentially, there are high amounts of T Regulatory (TReg) immune cells in fat tissue from lean people. These Treg cells regulate inflammation; inflammation directly promotes insulin resistance in fat cells. High amounts of adipose tissue have fewer Treg cells and thus higher inflammation, leading to insulin resistance.
This right here should be proof enough to anyone who doubts the fact that gaining body fat causes insulin resistance, not the other way around. You can gain copious amounts of body fat from over-eating almonds and avocado and induce insulin resistance.
That’s just the tip of the iceberg, there’s a ton I don’t know and it’s exciting to see how increasing or decreasing fat influences disease states and overall health.
It’s not hard to see that if you didn’t have any education on fat that it might be easy to fall for some marketing line. The insulin hypothesis did just that and caused many people (myself at one time included) to conclude that if carbohydrates raise insulin, and insulin limits fat burning and causes fat storage, that we need to be eating a low-carb diet.
Now we have tons of people who have success on low-carb (which is great!) with a few believing that you literally cannot get fat if all you eat is protein and fat because insulin is low. I’ve had this discussion many times with people, as I try to explain that the success from a low carb diet is because it controlled for calories and happened to be an intervention that fit their lifestyle. Same could be said for a low-fat diet.
Personal success does usually lead to personal bias, so it’s hard to convince anyone that they also could have had success on many different approaches.
My goal in this is to show exactly how fat storage and burning is regulated in the body, to reveal that dietary fat is in fact the macronutrient most easily stored as body fat while also being the least preferred fuel in the body. But you can still eat it and lose body-fat.
Here we go.
A Cookie a Day
I’m pleased to be able to share the following example to kick things off. Not only does it highlight that metabolism is dynamic but that are constraints applied to energy intake and expenditure in an effort to keep us healthy-weight stable.
“What would happen if you consumed an extra chocolate chip cookie (100 calories each) every day for 40 years? The amount of extra energy would equal 1.5 million calories. If we assume that there are 3500 calories/lb in adipose tissue, your weight gain would be 417lb over this 40-year period. Yet this clearly does not happen. If you really ate those extra calories, you would probably only gain about 6lb. After a short period of energy balance, the extra calories would cause you to gain weight (both fat and lean tissue) and your larger body size would increase energy expenditure sufficiently to balance the extra calories consumed.” – Sport Nutrition for Health and Performance, 2000.
Body Weight Regulation
I won’t get into all the details of metabolic adaptation, as I have covered it before in other blog posts. But the general overview is that with an increase or decrease in calorie expenditure, there is concomitant increase or decrease in metabolic rate.
Metabolic rate is comprised of more than just how much you weigh, although that is the largest factor: body size. In addition to that, you have the energy expenditure from digestion and absorption of food as well as activity. Non-Exercise Activity Thermogenesis (NEAT) is the largest adaptive component of your metabolic rate. You have a ton of sub-conscious energy expenditure such as nodding your head to music, tapping, fidgeting, getting up to go to the bathroom. You can also have changes in energy expenditure due to heat or cold stress, fear or anxiety.
The piece to remember is that the energy is always going somewhere. Calorie expenditure comes from metabolic processes. Aside from the calories that come from obligatory thermogenesis (all the energy required to keep you alive and running) the rest of your expenditure does come from movement. Conscious or subconscious.
As you change your calorie intake, the adaptive component of your metabolism works to maintain homeostasis aka “keepin’ it tight”. Lets say you decreased energy intake by 400 calories. Surely that is large enough to induce fat loss in a person, but are ALL those calories coming from fat? No. In fact, there is an adaptive component that reduces the amount of calories you burn other parts of the day in an effort to match the change in calories to keep weight stable.
When Calories Change
If energy intake goes down, energy expenditure usually will follow. You’ll start to fidget less on the couch, get up fewer times to use the bathroom or walk the dog shorter distances. All without thinking much about it. This is one of the reasons it can be so helpful to get clients to simply hit a STEP GOAL every day, to ensure they are still moving around enough.
The same goes for increased energy intake, you’ll probably start to move more and find yourself running a bit warmer, perhaps have an easier time putting on muscle. These are metabolic adaptations to expend energy to keep you from gaining to much weight.
Broadly speaking, when you eat less food, you expend fewer calories and when you eat more food you expend more calories.
Day to day changes in calories are inevitable and adaptive thermogenesis does a great job of regulating our expenditure around that. Naturally, persistent changes in calorie intake are going to result in body weight change. In the realm of excess calories, you’ll gain weight. This is why, aside from extreme medical conditions, if someone is obese, they are consuming the calorie that keep them at that weight.
What Eat vs What We Burn
Our physiology likes to keep things regulated, I am sure you’ve grasped that by now. When it comes to energy intake, we get most of our calories from protein, carbohydrates and fat. Under normal conditions, in weight-stable men and women (so no recent changes in weight) Thomas et al found that for both protein and carbohydrates, oxidation matched intake.
Oxidation is the “burning off” or energy expenditure side of the equation. So as you eat more protein or more carbohydrates, you pretty linearly burn more protein or carbohydrates. It’s extremely energy costly to convert protein to fat and it very rarely happens. Carbohydrates being the preferred fuel for the body are also energy costly to convert to fat and before they do, you’d probably need to start eating 500-700 grams per day.
Over-eating protein or carbohydrates also allows the body to spare protein, allowing for the accumulation of more in the body. This is one reason why it’s easier to gain muscle by overeating. But it also means that sparing protein for recovery is a top priority. Carbohydrates are preferentially stored as glycogen and most of the excess eaten is preferentially used for energy. De novo lipogenesis (the storage of any other nutrient besides fat as body fat) doesn’t occur in normal weight people. You’d need to consume an excess (such as the 500-700g per day above), done for consecutive days AND be in an energy surplus.
But if you weren’t in an energy surplus, you wouldn’t gain fat from eating preferentially more carbohydrates. So yes, eating carbohydrates stimulates insulin and insulin inhibits fat burning…but that doesn’t mean it’ll make you gain fat.
Periods of high insulin will inhibit fat burning but that doesn’t mean insulin is high all day. In periods where insulin is low, fat is free to be released from that fat cell to be used as energy. And if insulin is present, It doesn’t mean that NO fat burning can occur, just less. A low-carb and thus lower-insulin diet can surely work, but you have to be in a calorie deficit.
It can be frustrating to hear this information. It's hard to gain fat from eating more protein and carbohydrates AND insulin doesn't make us gain body-fat? Surely all we need to do is eat a low-fat diet? This is as far as people usually get before forming a conclusion but it's only half the story. In a way, calorie intake is the control switch for what happens with body-weight but the consumption of individual macronutrients (protein, fat and carbohydrates) determines more specific outcomes.
To find out just what the heck happens to dietary fat when you eat it, come back next week!