Despite all the success you might have had with the Primal way of life, doubts can still nag at you. Maybe it’s something you read, or something someone said to you, or a disapproving glance or offhand comment from a person you otherwise respect, but it’s pretty common when you’re doing something, like giving up grains , avoiding processed food, or eating animal fat , that challenges deeply-and-widely held beliefs about health and wellness. It doesn’t really even matter that you’re losing weight or seem to be thriving; you may still have questions. That’s healthy and smart, and it’s totally natural.
A question I’ve been getting of late is the effect of reducing carb intake on insulin sensitivity. It’s often bandied about that going low carb is good for folks with insulin resistance, but it’s also said that low carb can worsen insulin resistance. Are both true and, if so, how do they all jibe together? That’s what the reader was wondering with this week’s question:
I’ve been Primal for a few months now and love it. Lowering my carbs and upping my animal fat helped me lose weight and gain tons of energy (not too shabby for a middle-aged guy!). However, I’m a little worried. I’ve heard that low carb diets can increase insulin resistance. Even though I’ve done well and feel great, should I be worried about insulin resistance? Do I need to increase my carb intake? I always thought low carb Primal was supposed to improve insulin function.
Going Primal usually does improve insulin sensitivity, both directly and in a roundabout way. It improves directly because you lose weight, you reduce your intake of inflammatory foods, you lower systemic inflammation  (by getting some sun , smart exercise , omega-3s , and reducing or dealing with stress ), and you eat a wide variety of plants, animals, and herbs  with anti-inflammatory and/or insulin-sensitizing effects. It improves indirectly because you are removing the thing that exacerbates the condition – large amounts of carbohydrates – and thus avoiding the negative effects. You might still be insulin resistant, but since you aren’t cramming your face with carbs anymore, you don’t notice it.
And sure enough, the weight loss studies indicate that during weight loss, very low carb diets improve insulin sensitivity:
- In overweight women, a diet with less than 10% of calories as carbs improved insulin sensitivity , while a 30% fat, low-fat diet reduced it.
- In obese, insulin-resistant women, both high-fat and high-protein low-carb diets reduced insulin resistance , while the high-carb diet was not as effective.
- In obese kids, a very low carb diet was able to reduce indices of insulin resistance  along with bodyweight and body fatness.
However, going very low carb – to around or below 10% of calories, or full-blown ketogenic – can induce “physiological” insulin resistance. Physiological insulin resistance is an adaptation, a normal biological reaction to a lack of dietary glucose. As I’ve said in the past, the brain must have glucose . It can use ketones  and lactate quite effectively, thus reducing the glucose requirement, but at the end of the day it still requires a portion of glucose. Now, in a low-glucose state, where the body senses that dietary glucose might not be coming anytime soon, peripheral insulin resistance is triggered. This prevents the muscles from taking up “precious” glucose that the brain requires. The brain’s sensitivity to insulin  is preserved, allowing it to grab what glucose it needs from the paltry – but sufficient – levels available to it.
It appears that weight loss is the deciding factor, and since low carb diets tend to be more effective at inducing weight loss in subjects, they also tend to be better at reducing insulin resistance in insulin-resistant, overweight people. Once you’re lean and weight stable, though, very low carb diets (less than 10% of calories from carbs) can reduce insulin sensitivity. This is normal and totally necessary in the context of a very low carb diet. If we didn’t become insulin resistant while eating very low carb, our brain wouldn’t be able to get the glucose it needed to keep us alive.
Okay, but what about dietary amino acids? If our tissues are insulin resistant on very low carb, and insulin also promotes muscle protein synthesis , doesn’t that mean the amino acids from the protein we eat have a harder time getting into our muscles? You might think that, but that’s not how it plays out in the real world. In actual clinical trials, low carb diets are consistently linked with preservation of lean mass during weight loss . People on low carb diets lose more fat and less lean mass.
Muscle glycogen stores may be depleted, but if you want to fill those back up, you can do so quite effectively post workout, even when you’re low carb and otherwise physiologically insulin resistant. A bout of weight lifting , sprints , or even just regular walking  can improve your ability to tolerate and handle glucose by making you more insulin-sensitive. This holds true even for the otherwise insulin-resistant .
In the end, insulin resistance on very low carb appears to be a physiological adaptation to spare glucose for the brain and prevent your muscles from gobbling it up. I see no reason to think it’s a pathological problem, especially given the droves of success stories  on this site and others from people who have lost weight, torn up prescriptions, boggled the minds of doctors, and reclaimed their once-failing health through a low-carb Primal way of eating and living. I could be wrong, and time will tell, I suppose, but I doubt it.
Besides, there are far more pressing potentially negative influences on insulin sensitivity that we can be addressing, like:
- Sedentary lifestyles. And I’m not just talking about strength training and high-intensity sprints; simple, basic low-level physical activity, like walking on a daily basis, can have a powerful effect on insulin resistance.
- Unchecked and out-of-control appetites. Weight gain and an excess of energy (that the mitochondria can’t handle for whatever reason) are potent causes of insulin resistance.
- Environmental pollutants and toxins like BPA  and various fungicides  can have negative effects on insulin sensitivity.
To sum up, I don’t think you need to worry about insulin resistance as long as you’re still losing weight – which you appear to be doing – since weight loss exerts a powerful effect on insulin sensitivity. However, once you’re lean, or have stalled without changing anything, moving back toward the 100-150 Primal carb gram range will keep your insulin receptors “honest” without causing weight gain (and it may even jumpstart weight loss again ). Lifting heavy things, sprinting every once in awhile (in a manner suitable for your physical limitations), and doing lots of slow moving  will also keep you insulin-sensitive, particularly after the physical activity.
Thanks for reading, folks, and I hope I cleared this up for you without raising too many more questions. Let me know your experience in the comment section.