T Nation

Why Not Low-Fat?

I know the low carb vs low fat horse has been beaten to death multiple times, but I’ve genuinely been wondering about this for a while.

Why do most people seem to prefer low carbs for fat loss? I mean, for my understanding of how the body reacts to dieting, keeping the carbs as high as possible would only make sense.

Outside of helping with feeling fuller (which high protein and fiber probably are just as good at), why would a lifter prefer keeping fats higher at the expense of carbs? I can only think of positive things about higher carbs. Less overall glycogen depletion, less leptin depletion, better sleep and performance in the gym…

I’m not trying to bash on low carbs diets, there is no denying that those work and that any diet works for that matter if you adhere to it and it puts you in a caloric deficit.

Just interested in hearing your opinion.

I like fattier meat more than I like lean meat. I’ll be more compliant on a diet where I get to consume ribeyes and broccoli vs chicken and rice.

Pretty much the biggest factor for me. I also feel better on a high fat/high protein diet. When I eat high carbs, I feel bloated.


If you prefer high carbs then do it. Part of it is genetically influenced. About 1/3 of the population does very well with carbs at around 60%.

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Actually, I (and other proponents of “carb control” diets) recommend a fairly low intake of carbs on a “base” diet (about 25% carbs, 50% fat), but that during fat loss, calories should be removed from the fat intake since the body is basically going to be supplementing fat from stored body fat. The base diet is what you would eat if you weren’t “training” though it would account for your normal daily activity. And during a weight gaining period, or a period where training (which should be most of the time) added calories should come mostly from added carbs.

Let’s say that a base diet for someone not training then is
600 cals from carbs (150 grams)
600 cals from protein (150 grams)
1200 cals from fat
2400 cals total.

That is basically the maximum fat intake that you would ever use.

If you want to cut 600 cals a day, you would go to:

600 cals carb
600 cals protein
600 cals fat (the other 600 coming from stored fat).

If you want to add in an hour of resistance training you would add maybe 400 cals but mostly carb, such as 300 carb, 100 protein.

That would bring the “base” up to
900 carb
700 protein
1200 fat.

IF you want to do both you would be at
900 carb
700 protein
600 fat

So start with a 25/25/50% split using your resting or non-training caloric expenditure and then a) reduce fat intake for fat loss; b) add “periworkout” nutrition (carbs and some protein) for training.

I think that the reason that a lot of people recommend cutting carbs to lose weight is because the starting point involves people who are way above 150 grams of carbs or 25% while sedentary. The other reason is that cutting carbs will lower scale weight faster because of a reduction in water.

Reducing fat will improve insulin sensitivity as much as or BETTER that reducing carbs. People on high fat diets secrete far more insulin per gram of carbs ingested than people on low fat diets to the point where total insulin needs are virtually the same. If you burn 2400 calories a day, and you eat 1800, you will improve insulin sensitivity just as much if you cut the 600 from carbs or from fat. Cutting carbs may actually reduce low blood sugar by preventing rebound hypoglycemia that can lead to hunger.

OK the one problem can be that lower GI carbs often are more inflammatory or allergenic (such as beans or wheat versus white rice) but the key is to avoid large amounts of white rice etc. all at once and removed from periods of activity.


Can you link up this research? Sounds interesting. Thanks.

Practicality is a large part of it. “Eat low carb” is pretty simple to do and doesn’t require significant planning. Carb sources are pretty obvious, so avoid them. “Eat low fat” takes more prep, as many protein foods are also significant sources of fat, so reducing fat intake is inherently tied to monitoring or adjusting protein intake as well.

Dr. Clay Hyght did a solid job laying out the pros and cons of low carb vs low fat/high carb diets here. Thib talked about why he no longer advocates low carbs here.

Pretty sure @The_Mighty_Stu also prefers to keep carbs in play as much as possible and bring fats down a bit more.


In the US we were taught for many years to get lots of grains/breads/cereals and way less fats.

To cut carbs and increase fat is a rebel outlaw strategy that appeals to a lot of people.

Losing weight by staying in a caloric deficit while eating junk food is another strategy thats even more contrary to “conventional wisdom” and therefore cool.


Fat is good for you, if you went without it you’d die. I’m not talking about processed hydrogonized, homogonized, or rancid fats but as they occur in nature. I think the carb thing has a lot to do with the blood sugar and insulin roller coaster they put your body through. Any successful eating plan that tells me to cut carbs is secretly saying “stop consuming processed white sugar, processed white flour, and junk food.”

There are a lot of separate pieces of research that demonstrate that replacing carbs with fat reduces sensitivity to insulin by one or more of several mechanisms. One mechanism is that circulating fatty acids compete with blood sugar to get into cells by “covering up” glucose transport proteins. The second is that fatty acids in the blood may surround insulin and prevent it from acting. The third is that on a high fat diet, cells get “fat loaded” in place of having high glycogen content and the fatty acids in muscle cells take up space that glucose could be put. The fourth is that circulating fatty acids can physically block insulin receptors on the liver resulting in glucose being released from the liver and resulting in the liver making more glucose from protein (gluconeogenesis). The fifth, and probably the one that has the largest impact over a longer period of time is that when you eat less carbs, cells start making fewer enzymes to break down glucose for fuel. This happens on a low carb diet even if fat intake is not high.

I can’t really link to everything, but it is 100% established that replacing carbs with fat (without changing caloric intake) has only a fraction of the effect on reducing insulin released by the body than the fraction of carb reduction. People who went from 80% to 20% carbs for example (about 360 grams to about 90 grams) by replacing carb calories with fat still had about 75% of the daily total insulin release despite only 25% of the carb intake.

So hopefully you can start to look into it yourself, but here are some starters:


Many others, plus there are group studies that I have access too that are not available online-basically pilot studies showing that people who switched from high carb/low fat to low carb/high fat, or vice versa, while maintaining total calories consistently show a two stage switch in insulin sensitivity (one immediate and one that happens over 3-10 day) that ends up keeping total daily insulin secretion almost the same.

Ketosis raises relative insulin resistance (insulin needed to manage 1 gram of carbs or protein), but carbs (and protein) are so low at that point that total insulin levels are very low. In fact, the ketones make the body release more insulin that prevents insulin levels from getting below a certain threshold which is important because insulin signals many cell processes that keep you alive even in ketosis. Even in total ketosis on carb and protein levels generally considered to be optimal, daily insulin secretion is about half of what it is on a 50% carb diet, and even on ZERO carbs and protein, daily insulin secretion is 25%-33% of what it is on a 50% carb diet. Also important to note that high triglycerides cause (and are caused by) insulin resistance, but high triglycerides are produced mostly from fructose (sugar) and alcohol, not from ingested fat. Replacing carbs with fat has advantages, but it is important to know that replacing carbs with fat decreases sensitivity to insulin ALMOST equal to the decreased need of insulin due to eating fewer carbs.

Oh, another area you might look at is “physiological insulin resistance” which is basically a decreased sensitivity to insulin that occurs when carbs are replaced with fat in the diet.

I will mention that physiological insulin resistance is established in medical practice in at least 2 ways that I am aware of. One is that glucose tolerance tests are considered to be invalid if someone has not eaten at least 150 grams of carbs a day for the 3 days prior to the test because physiological insulin resistance can result in a failed test (blood sugar over 140 at 2 hours). Second is that fasting blood sugar over 90 is being considered as indicative of the beginning of pathological insulin resistance, but it is not an indicator if the person is on a low carb (<30%) diet because at less than 30% carbs, fasting blood sugar rises due to physiological insulin resistance.


If you look back at the 90s, plenty of people were doing great with low fat, high carb diets. Look at the diets of Mike Francois, Dorian Yates, and Jay Cutler. These guys ate buckets of carbs!

Many people back then did low fat, high carb.


Diets and training styles go in and out of fashion much like anything else.

As brick mentioned, some of the best physiques of all time dieted down low fat.


Thats a great post mertdawg


This study, performed 90 years ago clearly demonstrates progressive downregulation of glucose burning when carbs are excluded-even with a high protein intake. The peak blood sugars of 250+ would be immediately diagnostic of diabetes independent of the knowledge that the participants were on zero carb diets. The effect has been shown to manifest itself in less than a week, and largely abate in less than a week of a return to carb intake.

That’s interesting. Natural bodybuilder Kevin Stock recently published his blood work results after more than a year on strict carnivore. His fasting BG was 2.7mmol, i.e. almost off the chart (or, more accurately, not on the chart).

That is a little surprising since carnivore dieters typically report mildly elevated fasting blood sugar (100-110). I might expect it after a cut though, and people in fully adapted ketosis have had their blood sugar suppressed to <2 mmol/dL with no negative cognitive effects.

In ketosis, insulin still is secreted to keep ketone levels below a dangerously acidic level and hold down triglyceride and blood amino acid levels.

That is my own experience, the so-called ‘dawn phenomenon’. However, as you pointed out earlier, this is a lesser factor. It is cell sensitivity that matters in the grand scheme of things.

I tend to like higher carbs/moderate fat. That said, I’ve never had to lose a large amount of weight nor be “stage ready”. I feel much better eating carbs with each meal, and for me the main priority for working out and any dietary mainstays are the way it makes me feel.

I think people like low carbs because it’s so much more palatable to overweight people. You can eat burgers without the bun, bacon and eggs, coffee and butter (yuck), cheese and cream. And, if you’re overweight, you lose quite a bit of weight very quickly doing so.

If you eat high carb/low(er) fat, like pasta and grilled chicken, fruits and whole grains, beans and rice, you kinda have to eat healthy and chose foods many overweight people often avoid. So, you need to change your palate and avoid McDonalds.

I agree with CT in that carbs are awesome for performance and well-being. I eat carbs every meal, and fats from “real” foods like nuts and whole fat dairy. This is much more enjoyable than weighing foods and reading about insulin secretion (and I’m a PhD chemist).