Dear Mark: Vegetable Juicing, G_BOMBS, Blood Sugar, and Hot Workouts

Today is going to be a bit of a long Dear Mark blog post. I got some great questions from you guys. First, I cover three questions regarding the insulin spike and carb load from vegetable juicing. Next, I discuss the place of G_BOMBS, or the “perfect nutritional combination” of greens, beans, onions, mushrooms, berries, and seeds, in a Primal eating plan. The blood sugar response to meat is next, along with a followup question about how dietary fat affects the glycemic response to eating carbohydrates. Finally, I field a question regarding the utility of artificially increasing one’s propensity to sweat during workouts by turning the air conditioner off. Does it hurt? Does it help? Find out below.

Dear Mark,

I’m a big fan of the Primal Blueprint diet and lifestyle but I have a few questions for you about vegetables.

Lately, I’ve fallen in love with the nutritional content of vegetables. I try to eat them at every meal but in an effort to maximize my veggie intake, I recently bought a juicer and am experimenting with having fresh vegetable juice for breakfast. (And then I eat whole veggies at lunch and dinner, with protein and fat, of course.) So I wanted to ask you:

1. Does fresh vegetable juice cause a huge insulin spike in one’s bloodstream?
2. Would this spike be higher than if you ate the vegetables themselves (because you’re not eating the fiber at the same time)?
3. Would the number of carbs in the juice of one beet or the juice of one cucumber be the same as eating one whole beet or one whole cucumber?

I would still like to lose about 15 pounds of fat, so if you think my extra intake of veggies is going to cause my carb intake to skyrocket then I will think twice about continuing with the juicing.

Thank you for all your great work and thank you in advance for your advice!

Kind regards,


I’ll just run down the questions in order.

1. It totally depends on the vegetable you’re juicing. The main reason, after all, that I suggest you limit fruit juice is that it’s a huge bolus of sugar without the fiber and the satiation that comes from eating whole fruit. You can eat an apple and you’ll be pretty satisfied, but a glass of apple juice goes down like water, doesn’t really fill you up, and contains the sugar of four apples. That’s four times the sugar (and nearly four times the calories) with a fraction of the satisfaction. Sitting down to breakfast with a tall glass of apple juice, then, is like adding a bag full of apples to your breakfast.

Most vegetables don’t have that problem. Yeah, if you were drinking nothing but carrot and beet juice, you’d be getting a fair amount of sugar, but even a four ounce portion of carrot or beet only has about ten grams of sugar. And all the other vegetables you’re probably juicing, like lettuce, kale, chard, spinach, cucumbers, broccoli, are so low in calories and carbs that they’re not worth fretting over. Honestly, I wouldn’t worry too much about the carbs in vegetable juice.

2. Yes, the (insignificant) spike will be higher after consuming juice than after consuming the whole vegetable. In studies with whole fruit and fruit juice (very few, if any, studies are out there comparing vegetable juice to whole vegetables, so we’ll have to use the fruit juice research), whole fruit tends to elicit a lower insulin spike than fruit juice, an effect authors attribute primarily to the fiber. In fact, fiber has even been used in diabetics to help maintain their glucose control. That said, vegetable juice doesn’t have much sugar with which to spike your insulin. Again, I wouldn’t worry too much about it.

3. The number of carbs will be the same minus the fiber from the whole vegetable. If a beet has around 2 grams of fiber, that amount will be subtracted from the juice.

Although juicing vegetables won’t really affect your insulin levels one way or the other, I would caution that by discarding the fiber, you’ll be missing out on some polyphenols. Fruit and vegetable fiber isn’t “just fiber”; it also contains bioactive phytochemicals that may be of some use to you. Also, the effects of some polyphenols seem to be compounded when eaten with plant fiber, as is the case with apple pectin (a soluble fiber) and apple polyphenols. Overall, the fiber increases the bioavailability of plant antioxidants. Whole foods win again! Luckily, you state that you’re eating plenty of whole vegetables in addition to the juice, so I wouldn’t be too concerned. If you weren’t eaten the whole vegetables, I’d probably urge you to consider smoothies over juice, since smoothies retain the fiber.

I am hearing a lot about the G_BOMBS greens – beans – onions – mushrooms – berries – seeds as the perfect food combination. How does it fit into a Primal lifestyle?

D Brown

You’re asking whether greens – broccoli, chard, spinach, lettuce, kale, Brussels sprouts, dandelion greens, collard greens, mustard greens – are suitable for Primal eating? I eat some of those every single day.

You’re wondering if onions are okay on this plan? Yes, onions are great.

Shiitakes, buttons, whites, criminis, portabellas, boletes, chanterelles, morels, and select aminitas? Absolutely; mushrooms are the best.

Blackberries, blueberries, gooseberries, raspberries, loganberries, lingonberries, strawberries, boysenberries? Nothing like a fresh bowl of berries. Have at them.

How about seeds? Can you be Primal and still enjoy pumpkin, sunflower, squash, chia, hemp, and sesame seeds? Yes.

Yes, those are all excellent food sources for anyone. There’s this somewhat popular blog that’s even written a few articles on some of those foods:

Luckily for those on a Primal eating plan (and those people who share the bed with them), omission of the beans part of the G_BOMBS is both possible and advisable. Since you’re getting most of your protein from complete animal sources, you won’t be needing to rely on a stomach-disrupting, nigh-indigestible legume for the six or seven or however many grams of protein it offers. If you were on a vegan diet, you’d probably need to throw in some beans for protein. You’re not though. I therefore dub this new eating plan the GOAMBS diet: greens, onions, animals, mushrooms, berries, and seeds. And by “new,” I mean several million years old, of course.

Dear Mark,

Have you heard of the 80/10/10 (80% carbs/10% fat/10% protein) diet? Specifically it mentions eating a beef burger raising blood sugar levels.  And also claims without fat in the stomach that fruit, pasta, etc. raising of the blood sugar level is quicker and not a problem. Can you please address these (faulty) points? Love your blog and thanks for changing my diet and my life for the better!

Grok on!



Eating anything will raise blood sugar levels. That’s a normal physiological response to the introduction of food to your body. And sure, a “beef burger” will raise blood sugar levels, particularly if it comes with a bun, french fries, and large drink, but what are we really talking about here? Is it the “burger” part that’s causing a blood sugar spike, or is it the “beef” part?

I’d say it’s the former. White bread – of which hamburger buns are made – has one of the highest glycemic responses around. It averages around a 75 on the glycemic index. As for beef, it doesn’t even register on the glycemic index. There are no carbohydrates in ground beef; there’s nothing there to prompt a significant blood glucose response. It’s what you eat the beef with that causes the glycemic response. Interestingly, a beef burger, which has fat, protein, and carbs, will raise blood sugar to a lesser degree than a bun by itself. So, yes, a beef burger will “raise blood sugar levels,” but so what? Just about everything does. What matters is the magnitude of the increase. Lower is generally better.

And yeah, it’s true that eating a carbohydrate (like fruit or pasta) without fat will make for a quicker blood sugar increase, but as for it being “not a problem”? I beg to differ. It will make for a quicker and larger increase, whereas eating your carbohydrates with a fat (in the context of an actual meal with several different foods) will result in slower gastric emptying and a lower spike in blood glucose. Lower spikes – even if they’re more sustained – are less problematic. Higher spikes – even if they’re less sustained – are worse.

Postprandial hyperglycemia, a causative factor in vascular (and other health) complications, is defined as blood sugar greater than 140 mg/dl. As Paul Jaminet points out, eating carbs as part of a whole meal (with fat and protein and other nutrients) reduces the blood sugar response and prevents hyperglycemia. By all accounts, this is preferable.

Dear Mark,

I have recently moved to a very hot climate and our power generator (and thus air conditioning) only comes on at six. I have a friend who advocates working out without the a/c on because, in his words, “if you sweat more you get a better workout”. Is this true? It sounds like nonsense.



I see where he’s coming from, kinda. Harder workouts will generally cause you to sweat more, and harder workouts are “better” in some cases. The really intense ones are definitely more productive and effective, so it may feel like encouraging the sweat however you can is going the make the workout better. But it’s not the sweat that’s making your workout effective; it’s the work you’re performing. It’s how fast and how far you’re going, how much weight you’re lifting, how many reps you’re completing. The sweat is just an indicator, a byproduct of the true actor. And it’s not even a very reliable indicator. Sweat doesn’t always mean “effort” or “intensity.” You’ll sweat through a suit jacket just from walking outside in the tropics. Sweat simply means that your body is trying to cool off and reduce its temperature.

Since increasing the ambient temperature tends to increase sweating, we might use temperature increase as a surrogate for increased sweating. In fact there are a number of studies examining the effect of ambient temperature on exercise performance and fuel partitioning. Let’s look:

Increasing the ambient temperature during exercise increases serum lactic acid and reduces serum free fatty acids in trainees. Since lactic acid is a byproduct of glycogen metabolism and free fatty acids indicate the mobilization of body fat for energy, working out in hotter conditions may “burn less fat” than working out in cooler conditions. I doubt it makes a huge difference, but it might prove a helpful nugget of info for your friend.

Increasing ambient temperature may actually reduce voluntary workout intensity. In a recent study, cyclists were told to maintain a “constant rating of perceiving exertion” while scientists covertly increased and then decreased the ambient temperature in the room to see how power output changed. Although ambient temperature had a definite effect on voluntary power output, the behavioral alterations did not respond directly to the temperature fluctuations. A hot room probably makes you workout “less hard,” but it’s not a linear relationship.

All that said, it’s not the sweating that affects the exercise. If you really want to increase the effectiveness of your workout, increase the intensity. Don’t try to cheat by raising the temperature or wearing a thick black sweatsuit in the hot sun. You might cut water weight, but you won’t lose any more fat (and you might actually burn less of it) and you might reduce intensity without even knowing it. There might be a therapeutic placebo type effect going on with a hard sweat. Your friend might feel more satisfied or accomplished after a workout in which he sweated through the carpet, so in that sense he’d be having a “better” workout without the AC. If you enjoy your workout more or feel like you got more out of it because you produced a ton of sweat, I’d say you keep on doing it. The mental state is important.

That’s it for today, guys. Keep sending questions and I’ll keep answering them. Take care and Grok on!

TAGS:  dear mark

About the Author

Mark Sisson is the founder of Mark’s Daily Apple, godfather to the Primal food and lifestyle movement, and the New York Times bestselling author of The Keto Reset Diet. His latest book is Keto for Life, where he discusses how he combines the keto diet with a Primal lifestyle for optimal health and longevity. Mark is the author of numerous other books as well, including The Primal Blueprint, which was credited with turbocharging the growth of the primal/paleo movement back in 2009. After spending three decades researching and educating folks on why food is the key component to achieving and maintaining optimal wellness, Mark launched Primal Kitchen, a real-food company that creates Primal/paleo, keto, and Whole30-friendly kitchen staples.

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