The Green Stars Project

Are low-carb diets good for you? Sustainability and health benefits of carbs

Continuing on the theme of ethical consumerism and health, I’m going to take a look at the sustainability and health benefits of carbohydrates, and especially on the question of whether low-carb diets are good for you. But there’s a lot of material to cover, so I’m going to first look at scientific studies on low-carb diets and health.. Then, in the next couple of posts I’ll take a look at the Paleo diet (that should be fun!) and also at the weird and confusing world of gluten.

But how do low-carb diets relate to ethical consumerism? I hear you ask. Well, in part because the human population depends heavily on high-carb crops for sustenance and a shift from carb-rich foods to protein-rich foods can stress our planet even more, especially if that shift is towards animal-based protein. Yields per hectare of land are generally highest for carb-rich foods such as potatoes, corn, and wheat. Wheat, for example, provides around 20% of the world’s calories and has a small carbon footprint – see this post on bread for more detail. Like any product, of course, some versions are more ethical than others; for example I believe that organic wheat is significantly better than conventional.

Your annual carbon footprint from eating a loaf of bread per week is around 31 kg CO2, almost 50 times less than the estimated footprint (1352 kg CO2) from eating 1 kg of beef per week. They provide a similar number of calories.

So, there are two main topics in this post:

  1. Is reducing your carbohydrate consumption good for your health?
  2. Is a low-carb diet good for the planet?

I’ll tackle the health issue first and then briefly revisit sustainability (the latter requires a series of posts to do it justice).

Is a low-carb diet good for you?

A diet that limits consumption of carbohydrates can help you lose weight (temporarily). That has been the main focus of, and attraction to, the low-carb diets that emerged over the last few decades, from Atkins to South Beach to Paleo. But temporary weight loss does not equate to health – you can lose weight eating paint chips but that doesn’t make it a healthy diet. For a long time, I just took it for granted that there was a good body of evidence supporting the idea that low-carb diets make you healthier. You would imagine that these diets are prescribed by well-meaning experts who have your best interests at heart. In reality, what happens as a diet takes off is that these individuals morph into corporations selling an array of supplements, books, and food products. They don’t care how long you live; they just want you to buy their stuff.

Several studies have linked low-carb diets to weight loss, but no more so than a Mediterranean diet, and typically the weight goes back on after a year or two. The bigger questions, asked by a team from Harvard’s medical and public health schools in a study funded by the US National Institutes of Health, are:

Low-carb diet: impact on long-term health (mortality)

You would think that there have been many studies on this topic, but measuring the impact of diet on life and death requires long-term studies and it’s hard to control people’s eating habits over a long period of time. The Harvard group (Fung et al.) who published their findings in the Annals of Internal Medicine (2010), stated that there were really just two studies before theirs that looked at the impact of low-carb versus high-carb diets on mortality. A Swedish study (Lagiou et al.) found that women following low-carb diets had a significantly higher incidence of cardiovascular disease (CVD) mortality and a Greek study (Trichopoulou et al.) found a higher incidence of all-cause mortality (i.e., death, by any means) associated with a low-carb, high-protein diet. (I’ll show a chart later summarizing the results of all the studies mentioned here.)

Plant-based versus animal-based low-carb diets

The Harvard group asked the same question as the Swedish and Greek studies but they looked at one nuance: in a low-carb diet, do the rest of your major nutrients (protein and fat) come from plant or animal sources? Their conclusion:

In conclusion, consumption of a vegetable-based low-carbohydrate diet was associated with a lower risk of all-cause and CVD mortality whereas high scores for the animal-based low-carbohydrate diet were associated with a higher risk of overall mortality. These results suggest that the health effects of a low-carbohydrate diet may depend on the type of protein and fat, and that a diet including mostly vegetable sources of protein and fat is preferable to a diet with mostly animal sources of protein and fat.

This was a very big study (“…in up to 26 years of follow-up, we documented 12,555 deaths, of which, 2,458 were cardiovascular deaths, and 5,780 were cancer deaths.”) and the differences in mortality were large and statistically significant: The animal-based low-carbohydrate diet increased the risk of death by 23% while the vegetable-based low-carb diet reduced the risk of death by around 20%.

A low-carb, high-meat diet is less healthy

Another large study that compared an animal-based to a plant-based low-carb diet was published in the Lancet in 2018. They looked at a spectrum of carb intakes, from very low to very high, in over 15,000 adults. Their conclusion:

Both high and low percentages of carbohydrate diets were associated with increased mortality, with minimal risk observed at 50–55% carbohydrate intake. Low carbohydrate dietary patterns favouring animal-derived protein and fat sources, from sources such as lamb, beef, pork, and chicken, were associated with higher mortality, whereas those that favoured plant-derived protein and fat intake, from sources such as vegetables, nuts, peanut butter, and whole-grain breads, were associated with lower mortality, suggesting that the source of food notably modifies the association between carbohydrate intake and mortality.

You can see from the graphic below that a low carb intake is associated with the highest risk of death and that getting around half of your calories from carbs is the best option, on average. There was a small (10%) increase in mortality associated with very high carb diets, but they mentioned that this is probably due nutritional deficiency if your carb intake is too high (e.g., a diet that’s 90% composed of white rice). Note that they, like the Harvard group, found that mortality was higher when the fat and protein was animal-based rather than plant-based.

Impact of carbohydrate intake on mortality. The hazard ratio is the risk of death by any cause. Getting only 20% of your energy from carbs carries the highest risk: around 1.55 which means a 55% increase in chance of death. – The Lancet, 2018

Meta-analysis of health impact of low carb diets

In the same Lancet paper, the authors also conducted a meta-analysis of every qualifying study on the impact of carbs on mortality (which included all of the studies mentioned above). The findings from these studies are in good agreement with each other – as carb intake drops below 40% of your calories, your risk of death starts rising significantly.

Meta-analysis of the impact of low-carb diets on mortality. The Hazard Ratio (HR) indicates the risk of death by any cause. A HR of 1.75 (found in the Trichopoulou study, which looked the lowest carb intake) means a 75% increase in chance of death.

Risk of mortality from low-carb diets may be even higher in people who have lost weight

If you want yet another opinion on whether a low-carb diet is a good idea, check out this paper published Sept 2019 in the European Heart Journal that monitored 25,000 participants over 6 years. Their findings:

After adjustment, participants with the lowest carbohydrates intake had the highest risk of overall (32%), cardiovascular disease (CVD) (50%), cerebrovascular (51%), and cancer (36%) mortality. In the same model, the association between LCD (low-carb diet) and overall mortality was stronger in the non-obese (48%) than in the obese (19%) participants.

The message: you may get a little thinner but the odds of you dying increase by 32%. In fact, those that were thinner and following the low-carb diet had the greatest increase in mortality – a 48% increase in the odds of dying.

If you’d like to read more on carbs versus animal protein in your diet, take a look at The China Study, based on one of the largest dietary studies ever undertaken.

Here’s the bottom line on the impact of carbs on your long-term health:

Now I want to briefly take a look at whether low-carb diets are good for the planet.

Why low-carb diets can be bad for the planet

So, interestingly, the main problem with the low-carb diet from a health perspective overlaps with the main problem from a sustainability perspective: too much animal protein. As I’m sure you know by now, most animal sources of protein have the largest water, land and CO2 footprints of all of our food choices. On the other hand, the best sources of plant protein rank among the most sustainable crops because of their lower agricultural inputs and impact on soil health – particularly legumes (beans, peas, chickpeas, soybeans, peanuts, etc.). In recent posts on meat substitutes (tofu, Quorn, Beyond Meat, etc.) I described how the footprints of various plant-based (or fungal) proteins are significantly lower than those of meat. The same goes for plant-based milk versus cow’s milk, covered in a recent post.

So a low-carb diet can be in alignment with both health and the planet if it’s plant-based (e.g., rich in legumes). But a diet that includes a good amount of carbohydrates (around 50% of your calories) is probably the best option for both your health and the planet.

Are high-carb crops more sustainable?

It’s hard to be comprehensive here (and this post is getting long) but the general trend is that foods that are higher in carbs are more sustainable than foods that are higher in protein. By sustainability, I’m taking mainly about carbon and water footprints, yield per hectare of land, and pollution potential.

One broad reason for carbs being more sustainable than protein is that photosynthesis converts CO2 and sunlight directly into carbs, while the nitrogen in protein often originates from fertilizer that’s made from natural gas. It’s interesting to look at it from that perspective – when you eat carbs you are directly consuming CO2 that has been removed from the atmosphere, while eating protein often equates to consuming fossil fuels (except for legumes, which fix their own nitrogen from the atmosphere).

Potatoes are considered a sustainable crop. The FAO named 2008 as Year of the Potato, highlighting their low-water footprint and recommending sustainable farming practices to aim for, such as no-till cultivation.

I intend to write some posts on the world’s most sustainable foods. Oh wait! I just did a post on seaweed and that definitely qualifies as one of the most sustainable foods on the planet. I’ve also looked at the sustainability of high-carb staples such as wheat and potato (chips) and sustainable protein sources such as peas and soybeans. More to come.

Overall, we’ve gone astray by thinking that low-carb diets should be rich in meat. A diet higher in animal protein is absolutely linked to higher mortality – scientific studies show this over and over again. Most cultures around the world rely heavily on high-carb plants for their diet: wheat, potatoes, corn, rice, cassava, etc., and the concerning trend of not trusting carbs and incorporating more meat into diets increases the risk of severe climate change, especially when coupled with population growth. If you have been convinced that meat (even lean meat!) should be the foundation of a low-carb diet, then you have been deceived.

On that note, I’ll cover the paleo diet in the next post!

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