Why Eating Too Many Carbs Makes You Fat

Part 2 of a 5 part feature

Putting on Weight: Blame Carbs

| Apr 24, 2007

Carbs and carbs alone, not fat, increase body weight. It doesn't matter whether the carbs are from sugar, bread, fruit, or vegetables: They’re all rapidly digested and quickly converted to blood glucose.  A short time after a carb-rich meal, the glucose in your bloodstream rises rapidly, and your pancreas produces a large amount of insulin to take the excess glucose out.

Just as eating fat doesn’t raise blood glucose, it doesn't raise insulin levels either. This is important because insulin is the hormone responsible for body fat storage. Because fats do not elicit an insulin response, they cannot be stored as body fat.
Insulin takes glucose out of the bloodstream. It is converted first into a starch called glycogen, which is stored in the liver and in muscles. But the body can store only a limited amount of glycogen, so the excess glucose is stored as body fat. This is the process of putting on weight.

When your blood glucose level returns to normal, after about 90 minutes, the insulin level in your bloodstream is still near maximum.  As a result, the insulin continues to stack glucose away in the form of fat.  Ultimately, the level of glucose in your blood falls below normal, and you feel hungry again. So you have a snack of more carbohydrates, and the whole process starts over again. You're getting fatter, but feeling hungry at the same time. Ultimately, insulin resistance caused by continually high insulin levels in your bloodstream impairs your ability to switch on a satiety center in the brain. You enter a vicious cycle of continuous weight gain combined with hunger. Under such circumstances, it is almost impossible not to overeat.

Taking Off Weight:  Only Cutting Carbs Can Do It

So you've put the weight on–now you need to take it off again. Here again,  “healthy eating” hampers your attempts because a carbohydrate-based diet prevents you from losing excess fat. 

To lose fat, your body must use that fat as fuel.  It will only use its stored fat as fuel if you deprive it of its present supply of fuel:  blood glucose.

There are two ways to cut your body's glucose supply.  You can starve, which is what low-calorie, low-fat dieting is.  Alternatively, you can reduce the starches and sugars from which glucose is made, and make up the difference with another fuel:  fat.

The latter approach has two advantages over the traditional calorie-controlled diet.  First, you don’t have to go hungry.  Second, by feeding your body on fats, your body will stop trying to find glucose and will naturally begin using its own stored fat.

When you eat carbs, your capacity to use fat is limited. Increasing blood glucose during dieting stimulates insulin release. Even at very low concentrations of insulin, fat synthesis is activated and break-up of fat is inhibited.  This means that if you eat a carbohydrate-based low-fat diet, you force your body into a fat-making mode, not a fat-using mode.

Insulin inhibits the production of fat-burning enzymes, thereby preventing your body's fat cells from releasing their fat. This stops your body from burning your stored fat and makes it impossible for you to lose the weight you have put on.


1. Robertson MD, Henderson RA, Vist GE, Rumsey RDE. Extended effects of evening meal carbohydrate-to-fat ratio on fasting and postprandial substrate metabolism. Am J Clin Nutr 2002; 75: 505-510.

2. Bruning JC, Gautam D, Burks DJ, et al. Role of brain insulin receptor in control of body weight and reproduction. Science 2000; 289: 2122-5.

3. Odeleye OE, de Courten M, Pettitt DJ, Ravussin E. Fasting hyperinsulinemia is a predictor of increased body weight gain and obesity in Pima Indian children. Diabetes 1997; 46: 1341-5.

4. Sigal RJ, El-Hashimy M, Martin BC, et al. Acute postchallenge hyperinsulinemia predicts weight gain: a prospective study. Diabetes 1997; 46:1025-9.

5. Kreitzman SN. Factors influencing body composition during very-low-calorie diets. Am J Clin Nutr 1992; 56: 217S-223S

6. Meijssen S, Cabezas MC, Ballieux CG, et al. Insulin mediated inhibition of hormone sensitive lipase activity in vivo in relation to endogenous catecholamines in healthy subjects. J Clin Endocrinol Metab 2001; 86: 4193-7.

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Posted by Anonymous on 29 October 2007

ok..fat doesnt lead to a rise in the insulin level...but where will it finally go..simply pushed out of the system without a zilch of it being stored as body fat??? seriously hard thing to digest

Posted by Anonymous on 2 November 2007

The last comment/question from anonymous on Oct 29th, about where does the fat go ?? I have been wondering about the same thing.

Posted by TJPJE777 on 15 November 2007

Well I was the long winded one who made the post on Aug 3rd and on the high protein, fat, diet. My BD A1C was at 5.2%, my tri's were 1/2 of what is considered normal. My cholesterol ratio levels were an "amazing" 2.1 as my endo stated. When she found out that I was on a very high protein/fat/ etc diet she just said that I must have good genes. Three short months ago she wanted to put me on meds to lower my cholesterol and now she is just shaking her head at my results. I continued to loose weight and I am currently at about 165lbs a far cry from 248. Did it take hard work... oh yeah... was it worth it for my health... oh yeah... was it worth it for my children. I know it was!!

I think that the medical profession has to make sure that they re-look at all these preconceived medical thoughts that are out there and look at what really works. We are not all made equally as to how our bodies react to various foods so we have to work on a trail and error method.

If I eat fruit in the morning 1 banana and 1 apple my 2hr post is between 3.5 and 4.9. Others can have the direct opposite reaction. My father when he eats an apple his BG climbs to 13.0. This is why you need to test all the foods you eat and see how they will react to your body and condition.

Posted by Anonymous on 21 November 2007

"Carbs and carbs alone make you fat" In every seeming self evident nugget of dispensed truth there is a bit of truth but not the whole truth. The above commentary plays toward what people in todays society want to hear "I want lo carb" so I can eat my cancer causing meats, fats, oils, full fat dairy, without limitation because, let's face it, in our culture it is offensive to think at our level of affluence that we should be limited on anything.

Here Ph.D. Groves needs to read more. Carbs only may a person fat in a diet that has high fat. When fat is ingested it only takes 3% of its energy to store it. "Truely the fat you eat is the fat you wear" Indeed studies show that a syringe could extract fat from your person and it could be traced to if you eat trans fatty margerine, like fish, or eat chicken nuggest--it is stored so easily. On the other hand the body needing glucose as primary brain fuel, uses nearly 30% of carb calories ingested to make fat only in extreme circumstances. Which means this will not happen in most circumstances and then even if it does only 70% of the calories will be stored. This will only happen in extreme circumstances where someone ingest way more calories than needed like 3500-5000 calories for a person who only needs say 2300 calories. Sounds funny but do your own reading don't just trust someone like Groves pushing the easy eat animal products diet. Why because animal product diets may get you into ketosis but they cause cancer. Read the studies yourself at the National Library of Medicine (NLM) And the fat creation from carbs falsehood, search for 'de novo lipogenesis'

Ridiculous that carbs convert to fat so easily. Really what happens is people simply take in too many calories and then carbs are burned first, protein needed used (rest is always dicarded), and the fat (since there was enough carbs for that day) is stored for a future time of scarcity. A future metabolic dollar to the savings bank if you will. So will carbs make you fat, only if you are on a high fat diet. If you eat an only natural (the way nature made them) food diet with no added oils, margerine, butter at all. And keep your meat to no more than 1-2 oz per day. Certainly no fatty dairy products--maybe a bit of skim. Cheese the junk food is the worse. On such a whole foods, largely plant based diet with no added oils eating grains (yes), legumes, fruits, and beans.

You can eat as much as you want and still be okay even as a diabetic. The key the must be whole. Plain sweet potatoe with only a bit of salt and cinnamin on it. No fat. There is still natural fat in things 16% in oatmeal, 5% in peas, 9% in broccoli. They are naturally packages and will not cause a problem.

Reference: Volumetrics, John McDougall MD, Joel Fuhrman MD, Dean Ornish MD, Charles Atwood MD (pediatrician -- such eating is okay for kids over 2) Milton Mills MD Rice Diet

Read yourself the research, low natural fat eating that leans largely toward who foods like 100% whole wheat flour, beans, brown rice, will not cause upswings for most people. Refined white carbs are the problem.

I eat loads of bread. Lost nearly 25 lbs to a BMI of now 19.5 on my nearly 6 ft male frame. Don't gain or loose and eat as much as I want because I eat the right foods.

This is unpopular because people are hooked on salt, sugar, fat (aroma and mouth feel) and fat in particular is correlated over and over again to cancer--prostate, breast, colon, etc--check it out yourself but it must be a study that compares diets that are at least 15% different in fat. The Nurses health study was flawed in not really finding a high enough correlation because their low fat group turned out to be 29% (big deal) and the normal group was 36%. That is not enough of a difference. Don't believe me or Groves--read yourself.

I takes about 45 days at natural fat levels only to get rid of the desire for it. So effort is needed.

I am a person who has move my cholesterol and weight way down. Without drugs I moved my cholesterol from 240s to now the 140s by eating this way--take my cholesterol once a month. I eat this way the rest of my life--it is too good.

The best two reads on this are drmcdougall.com and drfurhman.com (Eat to Live) for free information.

Think I am out there? We'll see who is still fit and trim and healthy at 70, 80, and 90 like the okinawans, non smoking rural chinese and other vegetation leaning groups. Don't need to give up meat completely but only 10-15 oz a week for sure; lean too. Green vegetables in the studies have the highest correlation to cancer prevention along with reduction in fat particularly saturated fat.

Don't sacrifice you health for a short term weight loss plan because its popular. Some people used to think the world was flat too.

Stay well! Good health is earned not purchased.

Some great quotes...
--If it doesn't rot or sprout, throw it out
--If man made it don't eat it
--The fat you eat is the fat you wear
--Cheese is junk food (even low fat mozerella is 56% calories from fat whew)
--Choose food that fills you up not out (meaning with fiber! not a supplement; beans are great; yogurt and chicken breast have no fiber)
--People like to hear good news about their bad habits (like lo carb diets--eat more of those bad things.)

Most in this realm like Dr. McDougall can take 90% of type 2 diabetes (mellitus) patients off their meds within 30-60 days. Wow the freedom and reduction in heart disease, and amputation propensity but of course work in choosing to eat carefully. Being anticultural in eating is going agains the self medicating current culture (we medicate through our eating)

I am a person that has been saved by those doctors who are willing to serve others and not make a buck.

Check them out carfully and reason through to what makes common sense. Why when trim world peoples eat rice and beans doesn't get these chronic diseases like type 2 diabetes do we want to eat opposite and rich foods to put our selves in starvation mode (ketosis) an unnatural state? We do so because it is our human nature to not want to change or be uncomfortable.

Become educated, read all you can on many sides. Then take the plunge and try a whole foods, largely plant based, oil free diet for at least 30 days. You will be amazed at how you feel. It might even change your life permanently.

Have a wonderful life.

Posted by Anonymous on 15 February 2008

"Because fats do not elicit an insulin response, they cannot be stored as body fat."

So where *does* all the fat we eat go???

Posted by Anonymous on 22 February 2008

As a 60 year old female, I was diagnosed with diabetes early January 08. I have to thoroughly agree with the article. I have been counting carbs now since the week before Christmas and lost 23 lbs. My doctor also told me that he was quite happy for me to reduce my carbs to zero if necessary. Without doubt, I feel better in myself, less tired and in fact with more energy and the weight is coming off. My blood pressure has gone down from 190/100 to 130/87 and i just need to bring the lower level down. My eyes are getting back to my normal as I had some loss of visit 3 weeks ago.I know that carbs have always been my enemy and now obtain my carbs from green vegetables, such as broccoli, cabbage, sprouts, salads and not just lettuce, but cellery, raddish, peppers, cucumber, tomatoes. and have left out potatoes, rice, pasta,cereals except poridge, and everything to do with white flour. I eat the occasional slice of wholemeal bread about twice a week, eat crispbread instead and avoid all yeast products. I also watch the carb content of so-called good yoghurts whch are loaded with carbs. I have switched to soya milk and soya fats, soya yoghurts. I get oils from oily fish including kippers or smokes cod or haddock for breakfast and every other day poridge. The occasional grilled bacon, eggs, mushrooms, also enjoyed. My carbs during this time have ranged from between 25-35 grams per day and occasionally just 12 carbs per day. I enjoy such foods as smoked salmon, salmon, trout, lean chicken and turkey. My cholestral has dropped and so has blood sugar, and blood pressure. Who said dieting was boring. Counting carbs is not boring and it really does work. I can watch my weight reducing daily.

Posted by Anonymous on 5 March 2008

For an excellent description of "where the fat goes" (and much more), please read the book by Gary Taubes, which was published in Jan 2008 in the UK as "The Diet Delusion".

In the USA it was published in 2007 as "Good Calories, Bad Calories".

It is a long read, but worth it.


Posted by Anonymous on 1 May 2008

Another carb basher with no credentials soputing off..just what the world needed.

Posted by Anonymous on 31 May 2008

I eat a balanced diet but still I am very thin.What should I do extra to put on weight.My age is 21 and I weigh 55kgs??Please help.

Posted by Anonymous on 31 May 2008

In the presence of low glucose and insulin levels like those in a low carb diet, dietary fat not used for cellular repair and maintenance or other body processes like hormone production or muscle building, is either burned for energy or excreted. Same thing for protein, some of which is also converted to glucose by gluconeogenesis for use by the few body processes that can't use fat or ketones for energy. The conversion of protein to glucose loses almost half of the protein calories to the process. ie 50g protein converted to glucose yields less than 30g glucose.

Posted by Anonymous on 25 August 2008

25st 8lbs is what i weighed about 5months ago. I religously followed the Drs low fat/calorie & more exercise diets it got me no where.
I had to cope with them saying again & again you are at a seriously high level and soon you'll develop diabetes if you carry on. I did eventually get it but as soon as i got it it went, why?
I sceptically jumped onto a low carb diet not expecting any results but the weight was falling off me! The people in my street were noticing it and started to think i might be making myself sick! LOL!

Posted by Anonymous on 4 September 2008

wow that took a while to read through...good job people. here have a sticker for all your hard work *insert people grabing sticker here*. Now don't you all feel so much better. XD

Posted by Anonymous on 14 September 2008

For anyone who thinks low cholesterol (below 200) is good, check out Anthony Colpo's 2006 book: "The Great Cholesterol Con: Why everything you've been told about cholesterol, diet, and heart disease is wrong!" Really an eye opener. Also covers sugar, carbs, grains, vegetable oils, etc. The best book I've bought in a long time. LK

Posted by Anonymous on 24 September 2008

You should cut carbs, but not too much. You shouldn't mindlessly cut carbs, you're going to hurt yourself. I think article is overdramatic and rather un-informed.

Posted by volleyball on 20 October 2008

The article was pretty good. I do disagree with the premise as it is extremist and our bodies are not that way. But then you get the anonymous post 0f Nov 21 who is the opposite is really makes a good case for cutting the carbs because the rant on in the opposite extreme trying to save us from the author's view with their own opposite radical view. I've been to Okinawa, have they, do they know first hand? I doubt it or they would not make that statement.
These extreme views both fail to mention that we may all be human but the way we process foods is different. Natural selection has helped those who would thrive on the local diet. Now with the influx of world foods, we are eating things that do not agree with us and it is having a negative effect.
Lots of us thrive going low carb because that is what we have in our genes, just like there are those that may get worse going low carb.
For me the processed carbs are not agreeable with me, the cutting down of them has normalized my body. Low fatting it only made it worse. The chance of dying from cancer from meat is low, the chance of dying from diabetes is high. Therefore grill me a steak and hold the potato.
Lastly, I have little belief is a poster who claims to know everything and yet fails to post their name.

Posted by Anonymous on 1 November 2008

I have lost 20 pounds eating 70 carbs per day.
(For Diabetics: Try 45 carbs per meal x 3 meals and 15 carbs per snack x 2 snacks)

Leans meats and greens work!

-diabetic counselor

Posted by Anonymous on 18 November 2008

i have been sticking with "2,2,1" 2 carb choices for breakfast and lunch and 1 carb item at dinner. no sugar, no refined bread or white potatoes, and balance a fat/protein choice with carb choice to help slow the absorbtion of glucose into blood during digestion.

i have had type 1 for a year now, i am 23yrs old 6'2'' 188 lbs. muscle, college volleyball player. unless you are a long distance runner there is no reason to over eat carbs. 1 carb choice=20-28g carb containing item.

Do whatever works for your body and lifestyle, but try different approaches until you have figured out what is successful

Posted by Anonymous on 17 December 2008

Why is it people of all kind keep saying watch your carb intake, when i eat a pound of pasta ( no Cheese ) or a loaf of Italian Bread ( No Butter) i ahve been doing this for years and my weight does NOT go up. I personally think it is what you put on the carbs!

Posted by Anonymous on 23 June 2009

I totally disagree with this article. I lost 30 pounds in 3 months using the T-Factor diet and have maintained my reduced weight for 5 years running by eating less than 35 grams of fat per day while eating over 3500 calories per day.

My diet consists of:

- Cereal (1 gram of fat per serving variety)
- Skim Milk
- LOTS of Fruits and Veggies
- Boiled/Grilled LEAN meat like eye of round and chicken breast....
- Pasta + zero fat sauce
- Low Fat bread (most bread is low fat anyway)
- Water, V8 Juice, Coffee, Fruit Juice

I eat as much of the above as I want (which ends up at about 3500 calories and 30 grams of fat per day usually before I am stuffed)....

FACT...I have gained NO WEIGHT back in 5 years....
FACT....I still loose weight (about 1 pound per 2 weeks that I need to gain back..
FACT....I gain the weight back by increasing the fat content in my diet without eating more total calories.

Ask yourself a question.....Why is it so absurd that FAT in your diet ends up as FAT on your body....It's not absurd...It makes total sense.

Carb to Fat conversion requires a lot of energy...Energy that makes a calorie of carbs much much much less efficient at turning into fat than fat does. If you eat a little more than enough calories than your body needs with an excess of fat (meaning more than 40 or so grams) ALL of the excess fat goes into your fat cells. If you eat more than 100 calories in excess of your bodies caloric needs and you have about 60 grams of fat in your diet, you will end up with 10 grams of fat gained per day....In 44 days that is 1 pound....In 1 year that is 9 pounds....In 5 years that is 45 pounds and you are one big fatty!!!!

I'm telling you.....Keep fat less than 35 grams per day (LOOK AT ALL LABELS ON FOOD AND REALLY COUNT FAT GRAMS) and cut your calories just below what your dietary needs are and you will loose that weight fast.....

I guess I can believe the article IF and ONLY IF.....You only eat fat and keep carbs very low......I DEFY YOU TO HAVE ANY KIND OF NORMAL DIET THAT YOU CAN STICK WITH FOR 5 YEARS AND DO THIS!!!! Look at the foods I listed in my diet....Very heatlthy and normal stuff....Meat(LEAN), Veggies, Fruit, Bread, Milk (SKIM).....I can even have sorbet, italian ice, sweet-tarts, other non-fat type of desserts......AND I DO!!! I maintain EASILY with the diet above and I can tell you I am NEVER hungry. I do crave chocolate cake, pizza, fattening Ice Cream, hamburgers and hot dogs, etc....You can't eat most of those things on the diet suggested in this article anyway.....I just go have 3-4 bowls of chex cereal with skim milk and get over it though....

Anyway, if you want to end up as a fatso, listen to this article.

Posted by Anonymous on 26 June 2009

This doesn't make sense...Obviously the right carbs are needed for fuel and nutrients, like vegetables and fruit. We all know what a diet of protein and fat does to the human body.

Posted by Anonymous on 11 November 2009

What the low-carb haters refuse to acknowledge is that people on a low-carb diet are eating tons of vegetables. The key is that when you up your fat intake, you are LESS hungry, so you no longer obsess over food like you do with a low-fat diet.

I've lost 50#s on a low-carb diet, and I look forward to each meal with joy because I have such tasty and interesting food choices. My one struggle is getting ENOUGH calories. When you eat more fat, your body becomes satiated much earlier than with a low-fat diet.

What it comes down to, as long as I keep my carb total down, my calories can be whatever I want them to be..and I will continue to loose weight. That might be just anecdotal to some people..but it works..which is all that matters.

(And I'm healthier than I have been in a decade, Lower cholesterol, lower blood sugar, lower blood pressure)

Posted by Anonymous on 8 April 2010

If you're not physically active, you don't need many carbohydrates beyond what is necessary to get the fiber to make your digestive system run properly. Low carbohydrate diets are a reasonable adaptation for physically inactive people.

But don't pretend this is more healthy than athleticism and a diet rich in whole grains.

Posted by Anonymous on 16 December 2010

Beta oxidation is the process by which fatty acids, in the form of Acyl-CoA molecules, are broken down in mitochondria and/or in peroxisomes to generate Acetyl-CoA, the entry molecule for the Citric Acid cycle.

Posted by Anonymous on 4 January 2011

To the Anonymous post on 8 April 2010:
So what you're saying is that people who are physically active need carbs as fuel. This is actually not true at all. The human body's natural fuel source is fats, not carbs. Someone who is athletic can do just fine eating eggs, fatty cuts of meat, vegetables, and fruits.

Posted by Anonymous on 31 January 2012

To the anonymous post on 4 January 2011:

If someone who is athletic can do just fine eating eggs, fatty cuts of meat, vegetables, and fruits, then WHY do athletes BONK? Because they're "addicted to carbs," and therefore their bodies cannot utilize fat properly? If FAT is the body's preferred fuel source for everything except the few organs that require glucose, then WHY does the human body bother to store glycogen AT ALL? If protein can provide humans with all the glucose it needs, then WHY are human livers so TERRIBLY INEFFICIENT at glucogenesis (try eating over 300 g of protein / 1200 protein calories a day, you WILL BEGIN VOMITING UP YOUR FOOD) as compared to obligate carnivores? Even obligate carnivores such as lions don't naturally live in ketosis because their livers are five times as large as human livers in proportion to total body size.

Posted by Anonymous on 25 February 2012

Yea..Unfortunately all of the good, true, and useful information in the above article will be missed because the author made so many equally ridiculous claims. I think there needs to be an emphasis on not just cutting carbohydrates, as they are an absolute requirement, but rather emphasize the need to eat the "correct" carbohydrate (probably complex depending on the application), in small quantity (reduce the glycemic load), many times throughout the day. I haven't always been in decent shape, but now I eat the right carbs, at the right time, in the right quantities, and I'm around 8% bodyfat, with good lean muscle mass. I'm just trying to say there is two sides to the story...

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