Your Questions Answered: Low Carb vs. High Carb

Twitter summary: Answering questions on low-carb eating and long-term outcomes posed from last month’s column, www.diaTribe.org/dietbattle

It’s been tremendously gratifying to see the positive reception to my column last month, “Low Carb vs. High Carb - My Surprising 24-day Diabetes Diet Battle.” I was elated to hear that more than a dozen diaTribe readers have seen similar diabetes benefits with a lower carb diet: more time-in-range, less insulin, and less diabetes burden. Even a few people without diabetes have written in support of a lower-carb approach, or sincerely pledged to try it for the first time.

This article answers the most common questions I’ve received over the past two weeks, organized into three categories: questions on the experiment; questions on low-carb eating; and questions on long-term health outcomes (click on a question below to skip right down to it).

Eating fewer carbohydrates has been a serious game-changer for improving my blood sugars and reducing the burden of managing my diabetes. And since I started doing it five years ago, I’ve found it easier to maintain my weight, blood pressure, and cholesterol at healthy levels. That would be a remarkable combination for any diabetes drug or device!

All that said, there is not enough evidence in the reputable scientific literature to clearly validate what I am doing. The ADA’s 2014 Nutrition Therapy Recommendations note, “evidence is inconclusive for an ideal amount of carbohydrate intake for people with diabetes.” We’re sorely lacking high-quality studies on how different diets impact long-term health in people with diabetes. This is why I emphasized last month that this is an n=1 experience – patients should always check with a healthcare provider before making any meaningful changes to medication, diet, or routine.

I hope we see better research in the coming years – this is too important!

In the meantime, let me know what you think about this topic, and please keep sharing feedback on last month’s article!

Questions On the Experiment:
Did your weight increase?
Couldn’t you have improved your mealtime insulin dosing?
How were you affected physically and mentally by switching to “high carb”?

Questions On Low-Carb Eating:
What do you actually eat?
What about kids and teenagers?
How many meals do you eat every day?
What is the percent breakdown of fat, protein, and carbs you eat?

Questions On Long-Term Outcomes Eating Low-Carb:
Why do some studies suggest low-carb diets are similar to or worse than low-fat diets for weight loss?
Is low-carb eating healthy for improving long-term outcomes, such as heart disease?
What about kidney function?
What diet advice is a safe bet?

On the Experiment

Q: Did your weight increase? You used 34% more insulin eating high carb.

I actually don’t own a weight scale, so I’m not sure! If I had to guess, it probably didn’t change over 12 days.

I did feel hungrier on the high-carb diet, despite eating a similar number of calories – that might be because high-carb meals weren’t as filling as low-carb meals, or because it was a new style of eating. The high-carb diet also caused more hypoglycemia, and over time, that could lead to some additional weight gain from overeating to correct lows. But I’m not sure.

Some diaTribe readers have contacted me and praised a low-carb diet for reducing their own insulin intake and aiding with weight loss. One said, “A low carb diet is the only way I can maintain my weight or even lose weight, as I don’t need to use nearly as much insulin to get acceptable blood glucose levels.”

This is not surprising. Carbs are the king of raising blood glucose (far more than fat and protein), meaning a higher-carb diet is likely to demand more insulin than a low-carb diet to maintain the same blood glucose level.

Professional organizations like the American Diabetes Association (ADA) and American Association of Clinical Endocrinologists (AACE) always list weight gain as a side effect of taking insulin. A big advantage of eating low-carb, in my view, is the potential to take less insulin (lesson learned #3). That could translate into weight loss over time for some people.

Q: You switched to a brand new diet with foods you aren’t used to taking insulin for. Don’t you think with more time, you could have optimized your insulin dosing and insulin-to-carb ratio?

Dosing for high carb was a definitely a bit new to me, and I certainly could have improved! But in many ways, I viewed this as an “ideal” high-carb diet experiment – I measured every carb out, I wore real-time CGM, I took insulin before meals, I ate a whole grain, unprocessed diet without junk food or sugar, and I’m extremely active.

As Kelly pointed out in her accompanying editorial, real-world high-carb eating would likely incorporate more challenging circumstances than in this experiment. Many diabetes educators and nurse practitioners also wrote me to say that my high-carb phase was better than many of their patients do in the real world.

So while the bolus and basal insulin optimization could have been better, in reality, my high-carb results could have been far worse than I showed last month.

Beyond optimizing insulin, I hope I showed that a high-carb diet takes a lot of work, and it’s easier to get things wrong (lesson learned #4). It’s challenging to match the curve of insulin action to the curve of carb absorption, and as carbs rise, that task becomes more difficult! Insulin needs can vary widely from day-to-day and meal-to-meal based on activity, stress, sleep, type of carb, and so many other factors – those additional variables matter much more on a high-carb diet, because the insulin doses are much larger.

My insulin:carb ratio is one unit per 10 grams of carb, which is definitely not perfect. Nailing that number is absolutely critical on a high-carb diet, and many people need different ratios at different times of day. On a low-carb diet, a perfectly accurate insulin:carb ratio matters far less (lesson learned #5).

Q: How were you affected physically and mentally by switching to high carb?

Mentally, I was fried. I worked slower, thought slower, and got less done every day. I usually become grumpy and short-tempered when I’m high (>160 mg/dl), and foggy and slow when I’m low (<70 mg/dl) – both occurred more often eating high carb.

I also found a high-carb diet increased my feelings of diabetes failure and frustration (lesson learned #4). Of course, these feelings might have improved with more experience, but I’m confident the higher diabetes burden (e.g., measuring, counting, stress) would have remained the same. 

Physically, the extra hypoglycemia and hyperglycemia was exhausting. Exercise on the high-carb diet generally took more planning, as there was always more insulin on board to account for. I maintained a similar level of activity on both diets – eating more carbs didn’t seem to supercharge my energy to do exercise.

On Low-Carb Eating

Q: What do you actually eat?

See here for a longer column that answers this question, and here for my “Diet Commandments.” My diet is a lot of vegetables, nuts, seeds, lean meat, seafood, olive oil, lentils, and beans.

“Paleo” cookbooks tend to have many great low-carb recipes, though you have to steer clear of sugary ingredients like honey and maple syrup (which technically qualify as “Paleo,” but are definitely not friendly to blood sugar). Three recipe books that I use from time to time: Paleo Cooking from Elana's Pantry, Nom Nom Paleo , and Well Fed.

Though low-carb sounds extremely restrictive, using ingredients like zucchini, squash, and almond flour can approach what pasta, potatoes, and baked goods taste like – it’s a far less constrained diet than I appreciated when I started out!

Q: What about kids? My son is an active teenager and eats a lot of carbs!

I’ve written previously about the advice I would give my teenage self. I’m not sure 14-year-old Adam would have embraced fully low-carb eating, but my teenage blood sugars after meals would have benefitted from some tips:

• Take insulin at least 15 minutes before eating. By far the most critical tip for managing high-carb meals.

• Measure carbs out with a cup or scale. Eyeballing just doesn’t work, and going from package-to-hand is never a good idea.

• Cut carbs at breakfast – insulin resistance is high and it sets the tone for the entire day’s blood sugars. If there is only one meal to eat low-carb, this is it.

• The least damaging time to eat carbs is after exercise. A light activity like walking also works wonders after a high-carb meal (you may need less insulin; see here).

• Choose brown over white carbs whenever possible (whole wheat bread vs. white bread; brown rice vs. white rice).

• Eat fruit instead of traditional desserts (berries are best).

Q: You mentioned you eat 30 grams of carbs per meal or less. How many meals a day are you eating, since you averaged 146 grams of carbs per day?

I usually eat two to three meals per day accompanied by a lot of small snacks. Meals always have a lot of vegetables, and snacks are mostly nuts and seeds.

Carbohydrates do add up quickly when you count every gram. The 146 grams per day included fiber (~39 grams per day) and all foods with any carbs, including nuts, seeds, vegetables, and fruit. While half a cup of mixed nuts has ~17 grams of carbs (depending on what kind of nuts), they don’t tend to impact blood sugar very quickly, and I often don’t bolus for them.

Q: What is the percent breakdown of fat, protein, and carbs you eat every day?

The lower carb diet was ~21% of calories from carbs, ~26% from protein, and ~53% from fat. The fat calories were very high quality, plant-based sources: nuts, seeds, and olive oil.

As I noted last month, this is not crazy low-carb – people on the Atkins diet aim for ~20 grams per day and I averaged 146 grams/day. This diet is also not super high protein, which is often considered more than 30% of daily calories.

On Long-Term Health Outcomes Eating Low Carb

I’ve surveyed some of the scientific literature here, but I am by no means an expert. This section is not intended as a rigorous analysis of all studies out there. It’s also important to highlight that nutrition trials are hard to conduct well, typically too short, and confusing to interpret. The results often contradict each other, changes in one parameter automatically affect another (e.g., eating low carb automatically means eating more fat and protein – which variable influenced the outcome?), and studies are often observational with confounding variables.

Q: Why do I see studies suggesting low-carb diets are similar to or worse than low-fat diets for weight loss?

This is a very tricky topic, since weight loss studies vary widely in:

• The definition of “low-carb” – compared to the typical ~50% of calories, a low-carb diet could range from 45% to 10% of calories. That’s a big difference!

• What carbs were actually eaten – was it mostly fruits and vegetables, mostly starches, and how much snack food was there?

• Whether people actually stick to the diet – just because participants agreed to eat low-carb doesn’t mean they actually did.

• The length of the study and the comparison group.

So with all those caveats...

In a just-published analysis combining results from 17 randomized trials, low-carb diets were associated with significantly greater weight loss (~4 lbs better) vs. low-fat diets in overweight and obese adults. Renowned cardiologist and former FDA Advisory Committee member Dr. Sanjay Kaul co-authored the paper, lending credibility to the methods. Yet, 12 of the 17 analyzed studies were less than one year long, so it’s hard to know if these results would persist over time.

A different analysis published last year in the highly respected JAMA concluded that there are minimal differences between different diets for weight loss over 12 months. The paper advocates for recommending any diet that someone will stick to in order to lose weight.

That is perfectly reasonable. Weight loss requires patience and persistence in our modern food environment, and if a diet feels like torture, it will be hard to sustain long-term. And that is the key part, since most people regain weight when a diet ends. So the critical question is not, “Which diet is best for long-term weight loss,” but “Which diet is best for YOUR long-term weight loss?” This is why I’m a fan of eating commandments – general eating principles to live by rather than an exhausting short-term diet sprint.

Low-carb diets have a reputation of being hard to stick to, though some data suggests that might not be true. In an article in Nutrition published earlier this year, the authors note that adherence to low-carbohydrate diets in people with type 2 diabetes is “at least as good” as other diets, and is “frequently significantly better.”

Q: Can a low-carb diet reduce the likelihood of negative outcomes like heart disease?

We don’t know. That’s my conclusion after talking with experts and hours of reading the scientific data and available analyses. Most studies are too short (one or two years) or too flawed to draw meaningful conclusions about how a particular diet impacts long-term health. This especially applies to people with diabetes, where we really want to know how different foods impact long-term outcomes like the risk of complications.

But a few things seem clear. People with diabetes should choose diets and therapies that:

• Keep blood glucose in control (A1c <7% with minimal hypoglycemia);

• Prevent weight gain or enable weight loss;

• Maintain healthy blood pressure (less than 140/80 mmHg);

• Keep LDL cholesterol under 100 mg/dl, HDL cholesterol over 40 mg/dl in men and over 50 mg/dl in women, and triglycerides under 150 mg/dl.

There is some data that suggests low-carb diets can do all of these things, though the degree to which they succeed can depend on weight loss.

I have figured out a way for me to hit all of these recommended goals, and the lower-carb eating approach I described last month is definitely an important part of my plan, along with exercise and general discipline. Messages from diaTribe readers suggest it works for other people with diabetes, though of course, not everyone will experience these results.

Q: Doesn’t a low-carb diet put extra demands on the kidney from the higher protein intake?

Again, my conclusion is we don’t know. The American Diabetes Association’s 2015 Medical Standards state:

• For people with diabetes and no kidney disease, evidence is inconclusive for recommending an ideal amount of protein;

• For people with diabetes and kidney disease, reducing the amount of dietary protein below usual intake is not recommended (it does not alter glucose, cardiovascular risk, or the kidneys’ rate of filtration).

For context, the low-carb diet I discussed was ~26% protein, which is lower than many of the “high protein” studies (30%+ of calories) in the scientific literature, though a bit higher than the average ~16-18% in people with diabetes.

There’s also more to consider than just protein intake alone. If a low-carb diet improves blood glucose, blood pressure, or weight more than a high-carb diet, that could help kidney function.

As with many things, “it depends” on numerous factors. For caution, everyone with diabetes on a low-carb diet (particularly ultra-low carb diets) should inform their doctor and ideally have regular lab tests to monitor kidney function.  

Q: Okay, so there’s not enough evidence to make a strong recommendation for low-carb diets. But what should we eat? What diet advice is a safe bet?

• Eat less food overall

• Eat more vegetables and fruit (in that order)

• Avoid packaged food with long ingredient lists (red flag: ingredients you cannot pronounce or do not recognize)

• When possible, cook food at home instead of eating out (restaurant portions are usually too big)

Michael Pollan, who has been enormously influential to diaTribe and to me personally, puts it well: “Eat food. Not too much. Mostly plants.”