Calories and weight loss

To lose weight with­out feel­ing hun­gry, all you have to do is go ape, go wild, and eat plants. The easy and healthy way to lose weight is to fill up on high-fiber, low-fat plant foods and avoid ani­mal-based foods and oils. It’s also impor­tant to avoid processed foods that are high in fat or con­cen­trat­ed sug­ar but low in fiber. The only essen­tial nutri­ents that plants don’t pro­vide are vit­a­min B12, which comes from bac­te­ria, and vit­a­min D, which your body pro­duces nat­u­ral­ly when bright sun­light hits your skin.

Food rules for weight loss
Sim­ple rules for los­ing weight

A diet based on low-fat, unre­fined plant foods sat­is­fies your hunger on a rea­son­able num­ber of calo­ries. The high car­bo­hy­drate con­tent of the diet also helps you feel more like exer­cis­ing and even helps you burn more calo­ries at rest. It’s hard to “fat­ten” on a high-car­bo­hy­drate diet, because about 30% of the calo­ries are wast­ed when the body con­verts sug­ar to body fat.

Calo­ries are lost when sug­ar is con­vert­ed to fat

In oth­er words, the human body is well-adapt­ed to a low-fat diet based on unre­fined plant foods. We get weight prob­lems, as well as oth­er health prob­lems, when we eat foods that are low in fiber and/or high in fat, such as ani­mal-based foods and processed foods.

Why does “going wild” and eat­ing a more nat­ur­al diet help peo­ple lose weight? Wild ani­mals can’t count, so they nev­er count calo­ries. Nor do they ever sign up for step aer­o­bics class­es. Yet wild ani­mals stay at a nor­mal healthy weight while eat­ing what­ev­er they want, when­ev­er they want, and doing what­ev­er they feel like doing. Their secret is that they eat the right kinds of food. They eat the diet that their bod­ies are well adapt­ed for eat­ing. Thus, they can depend on their appetite to con­trol their weight. Like­wise, most over­weight peo­ple could eas­i­ly con­trol their weight if they sim­ply stopped eat­ing the kinds of food that are mak­ing them fat and filled up on low-fat, high-fiber plant foods instead.

A low-fat, high-fiber diet is the diet that the human body is well-adapt­ed for eat­ing. When we eat that kind of food, our appetite can reg­u­late our weight nat­u­ral­ly. Yet most peo­ple try to con­trol their weight while con­tin­u­ing to eat the kinds of food that made them fat. Instead of cor­rect­ing the kind of food they eat, they try to cor­rect the size of their por­tions, an approach that is prac­ti­cal­ly doomed to fail.

Calories are energy

The calo­ries in our food are real­ly what a chemist calls “kilo­calo­ries.” Each kilo­calo­rie rep­re­sents the amount of ener­gy required to raise the tem­per­a­ture of one kilo­gram of water by 1 degree centi­grade. Just to avoid con­fu­sion, I’ll refer to kilo­calo­ries as “calo­ries.”

All of the ener­gy in our food came orig­i­nal­ly from sun­light. Green plants use the ener­gy from sun­light to turn water and car­bon diox­ide into a sim­ple sug­ar called glu­cose.

The process of photosynthesis
Dur­ing pho­to­syn­the­sis, calo­ries of ener­gy from sun­light are used to con­vert car­bon diox­ide and water to glu­cose and oxy­gen.

The plant can then use the glu­cose for sev­er­al dif­fer­ent pur­pos­es. It con­verts some of the glu­cose back to car­bon diox­ide and water, releas­ing ener­gy that the plant then har­ness­es to use for oth­er pur­pos­es.

Glucose plus oxygen yields carbon dioxide, water, and energy
Glu­cose can be burned with oxy­gen to pro­duce car­bon diox­ide and water. This reac­tion releas­es ener­gy.

The plant can also use the glu­cose as a raw mate­r­i­al for mak­ing oth­er things, includ­ing oth­er car­bo­hy­drates (sug­ars, starch­es, and fiber), amino acids (the build­ing blocks of pro­tein), and fats.

The ener­gy that was used to make these big mol­e­cules out of small­er ones is stored in the big mol­e­cule. It will be released when the big mol­e­cule is bro­ken down again into small mol­e­cules.

Calories in food

All of the calo­ries in our diet came orig­i­nal­ly from plants. Plants make big mol­e­cules that have a lot of extra ener­gy embed­ded in them. Ani­mals eat those big mol­e­cules and con­vert them back into small mol­e­cules again. This releas­es the embed­ded ener­gy, which the ani­mals then cap­ture and use for their own pur­pos­es.

Some kinds of mol­e­cules have more ener­gy embed­ded in them than oth­ers have. Although fiber has ener­gy embed­ded in it, our bod­ies can’t break the fiber down into small­er mol­e­cules. As a result, fiber pro­vides prac­ti­cal­ly no calo­ries. On the oth­er hand, our bod­ies can digest sug­ar and starch, which pro­vide 4 calo­ries per gram. If we eat more pro­tein than we need, our body con­verts it to sug­ar and burns it for ener­gy. Like sug­ars and starch­es, pro­teins pro­vide about 4 calo­ries per gram. On the oth­er hand, fat pro­vides about 9 calo­ries per gram.

Calories per gram
Fat is a rich source of calo­ries.

Why does a gram of fat con­tain more than twice as many calo­ries as a gram of sug­ar or starch? The answer becomes obvi­ous when you look at their chem­i­cal struc­ture. Car­bo­hy­drates got their name because they are “hydrat­ed car­bons.” They con­tain one oxy­gen atom and two hydro­gen atoms (the equiv­a­lent of one water mol­e­cule) for each car­bon atom. In con­trast, fats con­tain almost no oxy­gen at all. They are main­ly a long string of car­bon, stud­ded with hydro­gen. It will take a lot more oxy­gen, and a lot more “oxi­da­tion,” to turn the fat into car­bon diox­ide and water. All that extra oxi­da­tion will release more ener­gy, which we mea­sure in calo­ries.

The chemical structure of glucose and oleic acid
Car­bo­hy­drates con­tain few­er calo­ries because they are par­tial­ly oxi­dized. Fats have more calo­ries because they are heav­i­ly reduced, chem­i­cal­ly.

Plants tend to be high in fiber, and their stored ener­gy tends to be in the form of starch. Food that comes from ani­mals nev­er con­tains any fiber, and it rarely con­tains digestible car­bo­hy­drates. In ani­mal prod­ucts, the stored ener­gy tends to be in the form of fat.

Why do plants usu­al­ly store starch while ani­mals store fat? It’s part­ly because the process of con­vert­ing sug­ar to fat is waste­ful. You actu­al­ly burn up some calo­ries in the con­ver­sion process. But this loss of calo­ries is a great invest­ment if you would have to waste ener­gy car­ry­ing your ener­gy stores around with you. A pound of body fat con­tains about six times as much ener­gy as a pound of starch and water. The only plant parts that are nor­mal­ly high in fat are nuts and seeds, which of course are built for trav­el.

How your body burns calories

To lose a pound of body fat, you have to burn up 3500 more calo­ries than you get from your food. The eas­i­est way to do that is to switch to a diet that makes you feel full on few­er calo­ries, so that you won’t overeat, and that encour­ages your body to burn extra calo­ries. A low-fat, high-fiber diet helps you do both.

Sugar and starch

Your body’s favorite fuel is glu­cose. The cells in your body use oxy­gen to turn glu­cose back into car­bon diox­ide and water, releas­ing ener­gy in the process. The cell then cap­tures some of this ener­gy and uses it for many dif­fer­ent pur­pos­es.

You can find glu­cose in some kinds of food, such as grapes. How­ev­er, most of the glu­cose that the body uses comes from the break­down of oth­er car­bo­hy­drates. Starch breaks down into pure glu­cose. Table sug­ar breaks down into a 50:50 mix­ture of glu­cose and anoth­er sim­ple sug­ar, called fruc­tose. High-fruc­tose corn syrup is a 45:55 mix­ture of glu­cose and fruc­tose.

Your body can store some glu­cose by con­vert­ing it into a starch called glyco­gen. When the lev­el of glu­cose in your blood­stream drops too low, the body reacts by con­vert­ing some of its glyco­gen back into glu­cose.

If you eat some extra sug­ar, your body will replen­ish your stores of glyco­gen. Once you have made enough glyco­gen, it could con­vert the extra sug­ar to fat, but it would waste 30% of the calo­ries in the con­ver­sion process. So your body prefers just to burn up a few extra calo­ries if you are eat­ing a starchy diet. This “mar­gin for error” can mean the dif­fer­ence between stay­ing slim and gain­ing weight.


Pro­tein can also be burned to pro­duce ener­gy. Your body can take the amino acids that are the build­ing blocks of pro­tein and burn them for ener­gy, in a chem­i­cal process called the Krebs cycle. Your body can even con­vert most of the amino acids to glu­cose, or blood sug­ar. The oth­ers can be con­vert­ed to oth­er kinds of fuel, such as ketone bod­ies or fat­ty acids.

Unfor­tu­nate­ly, there are two down­sides to using amino acids for ener­gy. Once the body has bro­ken an amino acid down and burned it for ener­gy, that amino acid won’t be avail­able for use in mak­ing new pro­teins. Also, con­vert­ing amino acids to sug­ar releas­es addi­tion­al waste prod­ucts, includ­ing ammo­nia and sul­fu­ric acid. If you burn a lot of pro­tein for ener­gy, then your liv­er and kid­neys will have to deal with a large amount of waste. That’s why high-pro­tein diets are bad for the liv­er and kid­neys.

Your body has no con­ve­nient way to store excess pro­tein. So if you eat any more pro­tein than you need, your body will just burn it for fuel. In oth­er words, excess pro­tein in the diet is real­ly just a dirty source of sug­ar. When you try to fig­ure out how much pro­tein peo­ple need, you have to con­sid­er how much of the pro­tein they eat is being used as pro­tein and how much is being con­vert­ed to sug­ar for use as calo­ries. Peo­ple who eat a lot of car­bo­hy­drate need sur­pris­ing­ly lit­tle pro­tein.

Peo­ple who eat high-car­bo­hy­drate diets end up burn­ing less pro­tein as fuel. The high­er the car­bo­hy­drate con­tent of the diet, the less pro­tein peo­ple will end up burn­ing for ener­gy, and the less ammo­nia and oth­er tox­ic byprod­ucts they will pro­duce. That’s why a high-car­bo­hy­drate diet has been rec­om­mend­ed for decades for peo­ple suf­fer­ing from liv­er or kid­ney dis­ease.

When peo­ple are starv­ing, they will end up using their body’s struc­tur­al pro­teins for fuel. It’s like burn­ing your fur­ni­ture and the sid­ing of your house for fuel. Although starv­ing peo­ple end up los­ing pro­tein from the body, the prob­lem results from not eat­ing enough calo­ries, not from eat­ing low-pro­tein food. Only under extreme­ly unusu­al cir­cum­stances do peo­ple who are get­ting enough calo­ries suf­fer from a short­age of pro­tein, or of any of the essen­tial amino acids.


Your body can also burn fat for fuel. How­ev­er, it prefers to burn the avail­able sug­ar first, sav­ing the fat for lat­er. If your body runs low on sug­ar, such as dur­ing star­va­tion or dur­ing a low-car­bo­hy­drate diet, you will end up burn­ing a lot of fat and pro­tein for fuel.

If you eat more calo­ries than you need, your body prefers to burn the car­bo­hy­drates first and then store the left­over fat. The fat can go straight to your fat cells. You lose only about 3% of the ener­gy when you con­vert dietary fat into body fat. That’s why fat­ty diets are so fat­ten­ing.

Some peo­ple try to lose weight by eat­ing low-car­bo­hy­drate diets, which means that they get a larg­er per­cent­age of their calo­ries from fat. Peo­ple often lose sev­er­al pounds dur­ing the first phase of the low-car­bo­hy­drate diet, because their body uses up its stores of glyco­gen. This releas­es sev­er­al pounds of water, which is then lost through the kid­neys. This weight will come right back as soon as the per­son starts eat­ing nor­mal­ly again. In the longer term, the low-car­bo­hy­drate diets “work” by mak­ing the body think it’s sick or starv­ing. The body responds by sup­press­ing the appetite.

Why did Mor­gan Spur­lock gain so much weight from eat­ing a fast food diet in his doc­u­men­tary Super Size Me? The food he ate was very high in calo­ries, and it con­tained a lot of fat as well as a lot of sug­ar. His body prob­a­bly used the sug­ar for his imme­di­ate ener­gy needs, and the left­over fat was effi­cient­ly stored in his fat cells.

Maintaining a normal weight

How do wild ani­mals man­age to main­tain a nor­mal weight with­out count­ing their calo­ries or sign­ing up for step aer­o­bics? They rely on built-in mech­a­nisms that reg­u­late their weight nat­u­ral­ly. When you trav­el around the world, you notice that some human pop­u­la­tions also seem to stay at a healthy weight nat­u­ral­ly. These pop­u­la­tions tend to base their diet on a starchy sta­ple such as rice or corn or pota­toes and eat a lot of veg­eta­bles and fruit. Unfor­tu­nate­ly, when peo­ple from those nat­u­ral­ly slen­der pop­u­la­tions move to the Unit­ed States and start eat­ing the rich and fat­ty stan­dard Amer­i­can diet, they devel­op the same weight and health prob­lems as the rest of the U.S. pop­u­la­tion. So the sim­ple solu­tion to our weight prob­lems is to switch to the kind of diet that is eat­en in places where peo­ple stay nat­u­ral­ly thin.

The soci­eties where peo­ple stay nat­u­ral­ly slim tend to con­sume a low-fat, high-fiber, plant-based diet. They usu­al­ly depend heav­i­ly on some starchy sta­ple, such as rice, corn, or pota­toes. They also eat lots of oth­er veg­eta­bles and fruit. This low-fat, high-car­bo­hy­drate, high-fiber diet works in sev­er­al ways to help reg­u­late weight. It affects both the “calo­ries in” and the “calo­ries out” side of the weight loss equa­tion.

As I explained above, fat is a con­cen­trat­ed ener­gy source. Not only does fat con­tain 9 calo­ries per gram (as opposed to four calo­ries per gram for car­bo­hy­drates and pro­tein), fat repels water. In con­trast, car­bo­hy­drates have only 4 calo­ries per gram and absorb water. That’s why a starchy food like rice end up pro­vid­ing only about 1 calo­rie per gram of food as it is served.

The human appetite is well adapt­ed to a diet that is low in fat and high in fiber. When over­weight peo­ple switch to a diet like that, they tend to lose weight effort­less­ly, because the sheer vol­ume of the food helps to sat­is­fy their appetite. The extra work that would be involved in overeat­ing doesn’t feel worth­while.

Besides reduc­ing the num­ber of calo­ries that peo­ple take in, a low-fat plant-based diet also tends to boost the num­ber of calo­ries that peo­ple burn up. That’s because most of the calo­ries are com­ing from starch. A starchy diet tends to make the body more sen­si­tive to the hor­mone insulin, which means that the glu­cose that is released when the starch is digest­ed goes quick­ly into the body’s cells. When lab­o­ra­to­ry mice are switched from a fat­ty diet to a starchy diet, they end up spend­ing a lot more time vol­un­tar­i­ly run­ning on their exer­cise wheels. Sim­i­lar­ly, peo­ple who switch from a fat­ty diet to a starchy diet end up burn­ing extra calo­ries, often with­out even real­iz­ing it. They fid­get more, or pro­duce more body heat.

Even though a healthy diet is high in car­bo­hy­drate, those car­bo­hy­drates should be more or less in their nat­ur­al form. The human body was designed to eat plants, includ­ing some sweet fruits. The sug­ar in those foods is bound up with fiber and water and oth­er good things, such as oth­er nutri­ents and antiox­i­dants. In con­trast, processed foods such as can­dy and soft drinks con­tain puri­fied sug­ar, with­out any fiber or oth­er added nutri­ents. So the ide­al human diet would be high in car­bo­hy­drate, but not high in added sug­ars.


Pho­to by the Ital­ian voice