Research has recently shown if you could only change one thing about your nutrition, adding vegetables should be that one thing. Most people think such advice stems from vegetables being so high in nutrients, meaning that they are so healthy. Others think that vegetables fill you up so you eat less of other things, cutting calories. While both true, neither is the reason for eating them shown in the new findings. Instead, vegetables are shown to make the rest of the meal healthier by slowing down the digestion rate of the entire meal, increasing metabolic rate significantly. If they are green leafy vegetables, then they can reduce body weight, body fat, and waist circumference significantly in both the short and long term. With weight loss being difficult in the short term, and particularly difficult in the long term, these findings indicate two things. First, vegetables have a large impact on health without changing anything else in your eating, and also the importance of having just one thing to focus on when trying to eat better. Trying to manage all the things that go into healthy eating can be overwhelming (water, types of fats, sufficient protein, vitamins and minerals, cooking versus raw, organic versus not, etc.).
To understand the studies, a quick note on how metabolic rate increases your quality of life. The studies were done with people suffering from type 2 diabetes, a condition that dramatically lowers metabolic rate (the number of calories burned throughout the day). In this condition, the body does not respond well to insulin, the hormone that tells all the cells in your body you have eaten and it is time for them to absorb the calories. When your body does not respond well to insulin, the calories go more to body fat. If the calories we eat go to body fat, those calories are converted into fat, stored as fat, and later burned as fat. Fat burns slower than the original nutrients, which is great for endurance, but not for intensive thought or movement. So we end up experiencing less mental and physical energy as we shift our calories to fat instead of our brain, muscle, and other lean tissues. The simple act of slowing down the digestion rate of our meals allows our calories to enter the bloodstream slower, giving our lean tissues more time to absorb and use those calories. When our lean tissues absorb and use more calories, we are burning more calories, and our metabolic rate is higher. This also means our brain and body is more active, so we are thinking and moving with more energy. All this at the expense of calories going to body fat, meaning we are becoming leaner. This principle allows body-fat reduction to occur while feeling better, with more energy, instead of the typical dieting that lowers your energy. Protein, fiber, and dietary fats all slow digestion to provide some benefits, but not nearly as much as vegetables do. Trying out different methods of eating may provide large initial benefits, in most cases simply from thinking about how you are eating, but much of the gains end up being temporary. Temporary changes are therefore called “fads” or “fad diets”. Vegetables, on the other hand, have a greater impact than any other single dietary change studies thus far, and have staying power.
The research showing just how powerful vegetables are came out in just the last few years. First, in 2011 is was shown that the one dietary change of eating vegetables before carbs leads to dramatically better metabolism (insulin sensitivity) in type 2 diabetics at 6, 12, 18 and 24 months (both the short and long term) compared to comprehensive healthy eating (a food exchange system, the standard of care for diabetics) [1]. This is not saying that eating vegetables along with junk food is better than over-all healthy eating. Instead, it is saying if you can change only one thing in your eating, change the one thing that has the greatest effect. Trying to change more things has the potential for even greater benefits, but that might become overwhelming and therefore lead to less benefit. Change is generally easiest if it is done one step at a time, and if only one step is actually ever needed for the effect you are after, even better.
The next study came the next year. In 2012 it was shown that it takes about 200 grams of vegetables (8 oz, which is 3 cups of lightly cooked veggies or double that in leafy greens) to significantly raise metabolic rate in diabetics [2]. If the vegetables were green then there was also a drop in body weight, body fat, and waist circumference. We tend to cook green vegetables less than those of other colors. Cooked vegetables are softer, so they would not slow stomach emptying and digestion as much, meaning their impact on raising metabolic rate would be less. In 2013 it was shown that having the vegetables 10 min before the carb resulted in dramatically slower meal digestion than when the vegetables were eaten 10 min after the carb [3]. This means having a lot of vegetables won’t help you slow digestion very much if you have already digested much of your meal before you eat them. It is shocking that 1/3 of the carbohydrate in meals is already digested and entering the bloodstream in just 10 minutes. This goes to show you how unhealthy carbohydrates have become in our toxic food environment in which everything is processed, and therefore digests faster than natural food. Fortunately, we have vegetables to save us from this mess. And the timing matters: If the vegetables are not in your stomach until later they cannot help you. Presumably eating vegetables together WITH the rest of your meal would be as helpful as eating them right before the meal, since either way the vegetables are in your stomach with the rest of the food, but this has not yet been tested. I personally choose to eat my vegetables together with the rest of my meals because it is easier to eat a lot of vegetables when you eat them with a tasty meal at the same time. Spinach tastes like pizza when you eat it with pizza. Kale tastes like a burger when you eat it with a burger.
Before all of these studies, in 2010, it was shown that the blood sugar excursion, meaning the rate that a meal digests and therefore how quickly blood sugar rises, is twice as good an indicator of cardiovascular mortality for diabetics than the standard measure used to determine whether or not they are diabetic to begin with (fasting blood sugar levels) [4]. This is profound. What it means is that you can be diabetic, on medication for it, but cut your cardiovascular morbidity risk in half by slowing the digestion rate of your meals. The subsequent studies (discussed in the last paragraph) showed you can cut your medications in half as well. Although adding a lot of vegetables to your diet might be challenging for a variety of reasons, it can be incredibly comforting to know that you can keep eating all of the other things you love and actually make physiological, medical, and quality-of-life headway without ever going on a diet. In fact, the effects are profoundly stronger than if you had gone on a diet. But you are still eating the things you love, to the point of fullness, with no restrictions. No deprivation, no place you can’t go to eat, no dish you can’t order. The only thing you have to focus on, and make sure happens every day, is vegetables. If you are not willing to make any changes in your eating, then this is a whole different issue. But if you want to make change, this one change might be the only thing providing enough benefits to not have to change anything else.
Changing what you love to do is hard, and in the long term practically impossible. Adding something to your life that you don’t particularly love (like vegetables) while continuing to do what you love (like pizza) is absolutely possible. Use what you love (eating things you like) as a trigger to remember to do what you don’t love as much (, meaning use the fact that you are eating to remember to add vegetables.
1. “A simple meal plan of ‘eating vegetables before carbohydrate’ was more effective for achieving glycemic control than an exchange–based meal plan in Japanese patients with type 2 diabetes” by S Imai et al., Asia Pac J Clin Nutr 20 2011 161
2. “Effects of total and green vegetable intakes on glycated hemoglobin A1c and triglycerides in elderly patients with type 2 diabetes mellitus” by K Takahashi et al., Geriatr Gerontol 12 2012 50
3. “Eating vegetables before carbohydrates improves postprandial glucose excursions” by S Imai et al., Diabet Med 30 2013 370
4. “Postchallenge Glucose, A1C, and Fasting Glucose as Predictors of Type 2 Diabetes and Cardiovascular Disease” by H Cederberg et al., Diabetes Care 33 2010 2077
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