Wednesday I explained why "butter is back" is not useful dietary advice, even when studies show that eating butter has little or no effect on disease risk (the total diet and calories are what matter). Now I can say the same thing about low-carbohydrate diets.
The debate about whether fat or carbohydrates is responsible for obesity has passionate advocates on both sides, although those for carbohydrates predominate in the press these days.
The main scientific model behind the low-carb approach is the "carbohydrate-insulin hypothesis," which journalist Gary Taubes, Harvard professor David Ludwig and others have extensively promoted. It suggests that a diet heavy in carbohydrates (especially refined grains and sugars) leads to weight gain because of a specific mechanism: Carbs drive up insulin in the body, causing the body to hold on to fat and suppress calorie burn.
According to this hypothesis, to lose weight you reduce the amount of carb calories you eat and replace them with fat calories. This is supposed to drive down insulin levels, boost calorie burn and help fat melt away … instead of just cutting calories, you're supposed to change the kinds of calories in your diet to lose weight.
To his great credit, Gary Taubes was willing to put this hypothesis to the test. He organized the Nutrition Science Initiative (NuSI) to fund studies that he must have hoped would demonstrate the benefits of low-carb diets.
To its great credit, NuSI recruited highly experienced and respected obesity investigators to design and conduct the studies.
The first of these studies has just been published. It fully discloses the role of NuSI.
Supported by the Nutrition Sciences Initiative … Nutrition Sciences Initiative (NuSI) convened the research team, helped formulate the hypothesis and provided partial funding. NuSI and its scientific advisors were given the opportunity to comment on the study design and the manuscript, but the investigators retained full editorial control.
In this case, because I am familiar with the work of some of the investigators, I'm inclined to take these statements at face value.
Here's what they did. They put 17 overweight or obese men in a metabolic ward and fed them a very low carbohydrate diet, so low that it would induce fat breakdown and ketosis. The calories were supposed to be sufficient to maintain weight, but were not. The men lost weight from water excretion and breakdown of body protein as well as of fat, as is typical of what happens during partial starvation. Energy expenditure did not increase to the level anticipated from the carbohydrate-insulin model.
The abstract concluded:
The isocaloric KD [ketogenic, very low carbohydrate diet] was not accompanied by increased body fat loss but was associated with relatively small increases in EE [energy expenditure] that were near the limits of detection [translation: barely detectable] with the use of state-of-the-art technology.
The discussion concluded:
Therefore, our data do not support the carbohydrate–insulin model predictions of physiologically relevant increases in EE or greater body fat loss in response to an isocaloric KD. However, it is possible that dietary carbohydrate restriction might result in decreased ad libitum energy intake—a prediction of the carbohydrate-insulin model that was not tested in the current study but deserves further investigation.
In other words, restricting carbohydrate does not increase body fat loss or energy expenditure but might help you eat fewer calories.
This result confirms some of the results of a previous study from the first NuSI author. That one, funded by NIH, concluded:
Whereas carbohydrate restriction led to sustained increases in fat oxidation and loss of 53 ± 6 g/day of body fat, fat oxidation was unchanged by fat restriction, leading to 89 ± 6 g/day of fat loss and was significantly greater than carbohydrate restriction (p = 0.002).
Taken together, these studies show that both low-carbohydrate and low-fat diets cause weight loss when calories are restricted, but low-fat diets cause greater losses in body fat content than do low-carbohydrate diets.
In my book with Malden Nesheim, Why Calories Count: From Science to Politics, we review a 1964 study that put obese patients in a metabolic ward and fed them low-calorie diets of widely varied composition. They lost weight at the same rate on diets ranging from 3 percent to 60 percent carbohydrate and from 13 percent to 83 percent fat. They titled the study Calories Do Count. The NuSI studies confirm the benefits of reducing calories from any source to lose weight.
- With regard to weight loss, calories count and the relative proportions of fat, protein and carbohydrate do not matter much (although low-carb diets may help with eating less).
- With regard to health, the food sources of calories matter very much indeed and nearly everyone would be better off eating less sugar—at the very least because sugars provide calories, but no nutrients.
EcoWatch Daily Newsletter
According to the UN Environment Program, up to 5 trillion single-use plastic bags are used globally each year, and because of the material they're made from, most municipal recycling centers don't accept them (more on this below).
The most sustainable option is to skip the bag altogether. You can also make your own reusable produce bags out of old T-shirts. But if you'd rather purchase them new, here are our recommendations for the best reusable produce bags on the market today.
Eco Joy<p>If you're making the switch to more sustainable shopping bags and want a variety of products to use, the <a href="https://www.amazon.com/Reusable-Sandwich-Biodegradable-Eco-Drawstring/dp/B003PK4W3I/ref=sr_1_36?crid=3TDUCB8ZOM7WI&dchild=1&keywords=produce+bags+grocery+reusable&qid=1613484643&sprefix=produce+bags%2Caps%2C189&sr=8-36" target="_blank">Eco Joy Cotton Reusable Produce Bags</a> set is a great place to start. The set comes with three mesh drawstring bags, three muslin drawstring bags, a large mesh tote and a zippered sandwich-size pouch.</p><p>Each product is made with organic, non-GMO cotton that's ethically sourced in accordance with Worldwide Responsible Accredited Production (WRAP) standards. The cotton comes from India and Turkey, and the bags are hand-assembled in Canada by the owner of Eco Joy, so you can feel good about supporting a small business while reducing your environmental impact.</p><p><strong>Customer rating:</strong> 4.7 out of 5 stars with over 300 Amazon reviews</p><p><strong>Why buy: </strong>Zero-waste; Handmade in Canada; WRAP compliant; Machine washable</p>
Organic Cotton Mart<p>Some shoppers prefer to use mesh bags when shopping for fruits and veggies. We recommend checking out <a href="https://www.amazon.com/Best-Reusable-Produce-Organic-Cotton/dp/B07CK2TJKL/ref=sr_1_16?crid=10A7NM0LQ0B7E&dchild=1&keywords=mesh+produce+bags&qid=1613483897&s=home-garden&sprefix=mesh+pro%2Cgarden%2C162&sr=1-16" target="_blank">Organic Cotton Mart's Reusable Cotton Mesh Produce Bags</a> if you're in this camp, as they're made with Global Organic Textile Standard (GOTS) certified cotton.</p> <p>Mesh reusable produce bags can make the checkout process easier than muslin bags since you can see what's inside them without having to open them up. Plus, the tare weight (i.e., the weight of the empty bag that should be subtracted from the total weight of your produce to make sure you don't pay extra for using your bag) is printed right on the label of Organic Cotton Mart's bags, making everything that much more convenient.</p> <p><strong>Customer rating:</strong> 4.6 out of 5 stars with nearly 1,000 Amazon reviews</p><strong>Why buy:</strong> GOTS certified; Machine washable; Biodegradable
Simple Ecology<p>On the other hand, if you just want to purchase muslin bags, we like <a href="https://www.amazon.com/Simple-Ecology-Reusable-Organic-Shopping/dp/B004UJ0U0C" target="_blank">Simple Ecology's Reusable Produce Bags</a>, which are also made with GOTS-certified organic cotton. Simple Ecology also has a <a href="https://www.amazon.com/dp/B01N6AUMBG/ref=sspa_dk_detail_2?psc=1&pd_rd_i=B01N6AUMBG&pd_rd_w=MA3ZS&pf_rd_p=cbc856ed-1371-4f23-b89d-d3fb30edf66d&pd_rd_wg=hVunQ&pf_rd_r=G6RTQ1Z5DKEY325MAJZ9&pd_rd_r=5d298b3a-1be7-4ebd-a9e1-d5d672a40497&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUExMzc4RVAxWjNLOTdCJmVuY3J5cHRlZElkPUEwNTc0NTAwMzBDMjFYOVJPTUpWSCZlbmNyeXB0ZWRBZElkPUEwNjYyOTM4M0s4Vk81SVBPS1NFSyZ3aWRnZXROYW1lPXNwX2RldGFpbF90aGVtYXRpYyZhY3Rpb249Y2xpY2tSZWRpcmVjdCZkb05vdExvZ0NsaWNrPXRydWU=" target="_blank">starter kit</a> that comes with several reusable grocery bags if you're looking for more variety.</p> <p>The benefit of using muslin reusable produce bags is that, unlike mesh, there are no holes for small items to slip through. This means that in addition to larger produce, you can use them to purchase bulk foods like lentils, beans and rice — or even powders like flour or spices — without worrying about anything leaking. They're also best for keeping leafy greens fresh.</p> <p><strong>Customer rating:</strong> 4.7 out of 5 stars with nearly 1,500 Amazon reviews</p><strong>Why buy:</strong> GOTS certified; Machine washable; Biodegradable; Sustainable Forestry Initiative (SFI) certified packaging when purchased from manufacturer
ECOBAGS<p>Whether you're buying bread, fresh flowers, produce or all of the above, the <a href="https://www.amazon.com/ECOBAGS-Market-Collection-Reusable-Natural/dp/B08KFGPGN5" target="_blank" rel="noopener noreferrer">ECOBAGS Market Collection Reusable Bag Set</a> is ideal for <a href="https://www.ecowatch.com/farmers-markets-coronavirus-safety-2645581711.html" target="_self">farmers market</a> shopping or large grocery hauls. The netted bags are durable, flexible, and pack down small so they're easy to keep in your car or purse.</p> <p>ECOBAGS is a woman-owned certified B Corp, which means it uses sound social and environmental practices. These bags come in packs of three or five and have a few different handle lengths and color options, but they're all made with GOTS-certified organic cotton.</p> <p><strong>Customer rating: </strong>Not applicable</p><p><strong>Why buy:</strong> GOTS certified; Machine washable; Biodegradable; Certified B Corp; SA8000 certified for the protection of basic human rights of workers</p>